funding. If you had clean, well-managed, safe places you may still have had a (rightful) backlash about the wonton nature of taking away people's rights at the time but the impetus was "we have to get people out of these hellholes."
it's a funny issue because it really crosses typical political ideologies.
You want more people in treatment? You're going to have to take their rights away. basic rights of freedom. A clear constitutional issue. Arguments will be made by one group that are typically used by other groups to get what they want.
Then people will see the "bill" for these services and say "don't take more taxes from me."
So, if you want less homelessness and you think institutionalization is th answer, you better be ready to go against 2 tenants of your ideology.