This will probably be an unpopular opinion but I think the reality is that the choice whether to be a landlord has no effect on the supply of housing and so is almost totally irrelevant to this essentially systemic issue. The only kind of stuff that matters here:

• Supply of housing influencing its cost
• Relative wealth of the poorest influencing their ability to pay for housing
• Other factors (the credit system etc) limiting people's access to housing
• Legal ability to use housing as a speculative investment and store of wealth (ie. low property taxes even if you own multiple properties)

The idea that people would buy property and then provide housing on a charitable basis in defiance of the market isn't realistic and isn't a viable solution to the problem. The only solution is to build the right incentives into the system. Someone can support the latter without trying to do the former.