This is not a question for which there is a straight answer, such as "which is the biggest city in India." It is a matter for discussion. I can only present my own point of view and there may be many other points of view also.
India has a secularist constitution. It does not have a state religion but promotes religious tolerance in its constitution. All the laws of the country are required to be compatible with this constitution, and the system of government. Pakistan, by contrast, is not secularist. It has a state religion, Islam, and was founded in order to be an Islamic state, and in reaction to a concept of India in which peoples of all religions would live together.
However, all societies are constantly in the process of change. The survival of secularism in India depends on how successfully nations set up systems of cooperation within themselves, or to what extent they are really more committed to competition.
Owing partly to the continued hostilities between India and Pakistan on the basis of religion since the foundations of these two countries in 1947, and the terrible civil war that gave birth to the two nations, secularism has not only been denied in Pakistan but severely challenged in India. What ensures that secularism remains the only viable rational option is that India is a multi-faith, multilingual country. Abandonment of secularism can only lead to more conflict and suffering for its peoples.
The Hindu Right has a long record of struggle going back one thousand years to the first Muslin invasions. The history of India has been in one sense a dialiectic between the struggle of wise rulers to construct viable secular states (such as Akbar 1556-1605) and the attempts to impose a state religion (Aurangzeb 1658-1707). Out of this struggle emerged a sense of proto-nationhood based on religion among the Hindu majority, starting with Shivaji´s war against Aurangzeb. The Marathas have always been on the militant Hindu Right, for this reason. Rajasthan is another conservative area with a strong tradition of Hindu Right militancy and a proud Hindu militarist tradition. Elsewhere, where majority Hindus have to share space with significant minorities, especially Muslims, such as Gujarat, communal traditions are strained. Furthermore, the forces of the Hindu Right such as the RSS, VHP and their political party arm, the BJP, are all determined to impose Hindu majority rule to replace secularism in real terms, even though in terms of the constitution they remain secularist. In other words, BJP says that everyone can live in India provided they recognise that Hindus (meaning caste Hindus) come first and no conversions are allowed. This is not in the spirit of secularism as real secularism means that the government does not interfere in the free choice of individuals to decide where their faith affiliation lies.
The Congress Party has always been committed to secularism but its vote base has become increasingly dependent on that of minorities - Dalits, Muslims, scheduled castes, Christians etc. - who feel increasingly oppressed by the aggressive fascistic stance of the caste Hindu majority. The caste Hindu majority feel justified in this stance as they feel that in the attempt to build secularism in India, the needs of the majority have been left out over the more than half century since Independence in 1947.
There are two unresolved major problems rooted in India´s history for over one thousand years that underlie the struggles and conflicts in the Indian sub-continent today. One is the relationship between Hinduism and Islam. Kings, emperors, the British colonialist rulers, terrorist groups and modern politicians have mostly done their best to ensure that two religions cannot get along. Out of the conflicts they generate, they derive their power. The more trouble they are able to cause between the communities, the more they strengthen their hold on power. India and Pakistan as two states were actually born out of that very process of division.
Yet India has been enormously enriched and expanded in its development as a civilization out of the communication between the two civilisations. The The Agra Fort, the Sikh religion, Mughal painting, and Indian classical music are examples of the high points of this cross-fertilisation of two faiths. In many places in India, Hindu and Muslim communities have lived together in peace and friendship and learnt from each other. Then the politicians step in, create suspicion and hatred, and things fall apart.
The other factor is the struggle created by poverty and scarce resources. British colonialism increased the poverty of the Indian agricultural sector enormously as well as destroyed the Indian crafts industries - this is well-documented. The wealth of India was drained to build the palaces and castles of the "nabobs" who went back to England. The British aristocracy and the upstart "nabobs", between them, exploited both the British working class and the Indian masses.
The disparity in living standards between rich and poor in India reaches desperate levels and there are signs that it is getting worse. As India´s national income is reaching for the skies, the rich are becoming a much bigger class than they were and much richer. The absolute numbers of the poor, both rural and urban, are getting greater. Global communications have brought into the homes of the average poor Indians what the lifestyles of even ordinary people in wealthy nations are like, creating discontent. In the cities, poverty and detachment from village communities is creating insecurity and discontent as well as a breakdown in traditional cultural values. All this is effective breeding ground for the work of anti-secularist politicians.
Until it becomes clear through increasing awareness of the masses of BOTH countries, India and Pakistan, how they are being exploited by their leaders, how they are being made to compete and struggle with one another instead of fiding ways of cooperating in the common interest, secularism will remain in a state of tension. It cannot be eliminated, since India cannot function without it. If any party tried to really make India into a national Hindu state, it would lead eventually to civil war WITHIN India. But nor can secularism solve the problems of the country without, first, secularist governments making a serious effort to solve the problems of the Hindu majority by taking a strong line with the black economy and using the money to redistribute wealth to the masses of the Hindu majority. Second, Pakistanis will have to persuaded to abandon the Islamic state. This cannot be done without a revolution of some sort, since Pakistan was founded as an Islamic state. The Punjabi Pakistani landlord class stays in power and dominates its masses and its minorities (Baluchis, Sindhis, Pathans, all Muslims also) by stressing the conflict with "Hindu India" and diverting attention from its terrible problems of poverty and inequality. The Right wing always seeks diversions such as religious and national conflict to persuade the masses to make common cause with their own oppressors, the economic elite classes. This helps these very elite classes to stay in power.
In India, the elite Hindu landlord classes in the countryside use their high caste status combined with violence to suppress the ordinary cultivator, especially Dalits, Scheduled Castes and Muslims. They persuade the poor, struggling caste Hindu cultivator that at least they are of higher status than these minorities. Thus, social identity and status is used to blur the realities of class exploitation using the trap of caste status to give poor Hindus something to believe in and belong to and forget the reality that they are exploited by the landlord and moneylending classes.
When people all over the Indian sub-continent realise that cooperation and sharing, not competition, among their masses, are the answer to the problem, they will give up the drugs of religious conflict and the caste system and work out a new order. They will have to tackle the REAL problems of the Indian sub-continent - the problems of class, caste and unfair distribution of wealth. Hindu or Muslim, Christian or Dalit, all need to work together for this and kick out the landlord and moneylending classes that feed off them and use the very real record of religious and community conflict in the historical record to powerfully strengthen their position by setting various sections of the masses up against each other.
Secularism is a great ideal and a NECESSARY one for India to be a success. But for it to succeed in the end requires a transformation or resolution of all the historically rooted problems of India. This can only come about through awareness and this awareness reaching into the masses and cutting through the lies and manipulations of the politicians and vested interests.
It would also require in the end a REVERSAL of the settlement of 1947. Pakistan would have to disappear and a single INDIA be born again, firmly committed to fair distribution of wealth and harmonious relationship of communities of all faiths and persuasions. This requires cooperation from both Hindus and Muslims. The Hindu Right and the Islamists would have to be sidelined as terrorist groups and increasingly isolated and picked out by a powerful secularist state committed to the well-being of all communities and enjoying the support of the masses on both sides of the religious divide.
I think we are at least 150 years away from anything like this! Right now in India we are a secular state trying desperately to fight off the deadly work of communalist politicians, an aggressive caste system, while in Pakistan Islamic backed by the armed forces and supported by the landlord class keeps secularism at bay.
There is no way secularism in India can really strengthen its position beyond a lofty ideal enshrined in the constitution until Pakistan itself has "withered away."
Of course,yes and it is the secret of 60 Years of Happy democracy.From past to present no one religon kept at the top of the table or no one is under the table.From the case of Ram janmbhumi Babri mazid to the case of Ramsatu bibad the Gov looked all the religions from one and only one eye.