How might laws tolerating other religions have affected the spread of Islam among the population?

Answer 1

By tolerating other religions since almost the beginning, the Islamic people were able to talk to other non-Islamic about religion. Some of these people might have then thought Islam was better than their religion and converted

Answer 2

The toleration of religions other than Islam in areas under Islamic control made the spread of Islam among the population slower. It took a few centuries before the areas under Islamic control were majority-Muslim regions. Conversely, Christianity, which often took a more active role in forcible conversions would achieve Christian-majority in conquered regions within a few decades.