I would want to screen the person for why they are homeless, what they are doing, not just planning on doing, to get an income, will this hoped for income be 3 times the rent?

You can still apply your normal screening criteria. 

Landlords need to be transparent about their rules and make sure they are screening their tenants, and renters should be respectful and understanding of the policies.

Strong pass, don't waste any more time screening.

What happens when you drive all of the tenants out, or you fail to properly screen new tenants and after 5 years you have 50% vacancy (or worse)?

Yes, one roof, one door but less turnover costs (vacancy, advertising, turn over rehab, tenant screening), someone taking better care of your property, appreciation vs multi, and more ease of selling when the time comes.

I wouldnt use it as a way to screen properties.

I screen my tenants and most stay 5 years or longer.  

While screening alternatives, be clear with your expectations; time of response, repair solutions (new or repair), reasonableness of costs, how do they vet contractors/repair companies.  

If you pay 300 a month for a year you will have gained an extra 3600 in equity, but that equity isn't going to help pay the bills when the tenant moves out and the property sits vacant for a month while you replace the carpet and screen a new tenant.