My thoughts are that in general, they fall into 2 groups:
1. Mentally disabled
2. Drug addicts
I have an uncle who is homeless. Started smoking meth and decided he didn't want to work anymore after living in his mom's basement for 5 years.
He had all the support and help from family a man could dream of. Turned it all down to keep smoking meth.
He lives in a tent in the woods now.
If my uncle decided he should pitch a tent in a public park or on a sidewalk, I would say remove him immediately.
There are lots of homeless people who turn down shelter because they can't do drugs there.
If you choose to live on the street, create an unsafe environment and generally make a place shittier, society should be able to remove you from those places.
Skid row is a great example of what liberal softness leads to. And just the general state of LA or SF.