Well, it became unethical after everyone who had huge budgets bought up all the property, displacing everyone who couldn't. In a sense, it's a question of the ethics of owning property being inherently displacing. If there is only private property that nobody wants others on, and public property that isn't housing and nobody wants others on, then you're kind of both screwed and you're subject to the consequences of the system that let you have those things in the first place.
I'd rephrase this in what I think is a more succinct way. It's unethical because you're profiting off of displacement, in a system that allows you to do so, then being mad when the displaced don't care about the system that doesn't care about them, and so they take it back by setting up on your doorstep. Whatcha gunna do rich boi!?
