Why did socialists think that private ownership of the means of production was bad?

Answer 1

Socialists - today mostly called social-democrats - never were against private property as such. They only protested (especially in the early 20th century) against the sometimes very unequal way in which wealth in some countries was divided and against the lack of care for people who could not provide for themselves - the lack of social security, basically.

Even the Communists were not against private property as such, but they had a habit of taking away property from people who were considered 'capitalists'.

The 'ideal' of a community where no-one had any property so that all property was communal and where people were given an income according to their needs, where a larger income was almost excusively based on a family being larger of members needing special care, was never put into practice anywhere. Only North Korea comes close but of course the ruling elites there have no lack of property, income and perks.