Adopting homeless people has one main problem with it. Most people who are homeless are so because of drugs or alcohol abuse. This is not all of course, but for the most part they would rob you blind given the opportunity.
As for dogs most would never even consider hurting anyone unless they felt that they or thier owner was threatened. I have been in bed for the last 20 hours sick over who knows what, and everytime I woke up I had my nice cuddly friend pressed up against me with her head on my shoulder. Not once did she wake me up, but it was comforting having her there. No homeless person, or even normal person is capable of that type of love.
Plus it would feel odd if I woke up and had a homeless person rubbing up against me!