Almost without exception each one of these homeless have burned through all the good will their families and friends have overabundantly extended. Their families are FRIED to the point of exhaustion.
There may be a few that we passed out there on the streets who are so mentally ill that they are incapable of accepting help but, as you say, the rest are addicts, thieves, and liars.
I know from whence you speak, all too well. I have a few relatives that meet that description. They've burned every last ounce of trust and credit they ever had with their kin.
It can be a hard and painful choice, but there are times when you just have to cut the cord.