In my experience, they're inexperienced with the world and of a background where problems like these are only hypothetical, and therefore very black and white. It's easy to get behind the feel-good answer if you know nothing about the problem other than a Vox explainer you read 5 minutes ago. They don't know what real harm reduction actually looks like, because that would take more than hitting Like and Share.

"Wow! Homeless people still exist! In my city?! That's not very nice! And the police threw away the cover photo lady's tent and pepper-sprayed her friends sleeping bag? That's really not very nice! All to clean up the area for the visit of some official?"

The violence with which many camps are removed is abhorrent to many, as is the idea of shuffling them around for mere cosmetic purposes (not to actually get them into a better place), so there's a naive "everybody be nice! leave those poor people alone!" attitude that doesn't actually care about pesky details.

Since their experience is hypothetical and they're idealizing and romanticizing The Homeless, discussion on practical realities like the number of violent felons and sex offenders in camps is shut down with a classic "that never happens". They'll pretend it's some kind of made-up minority and not the bulk of people who can't/won't go to a shelter (i.e, because they have warrants or have been banned for bad behavior).

Sure, they got what they asked for, but I don't believe they ever really considered what they were asking for, beyond "stop being mean".