Then why don't we allow co-ed housing?
It's because we don't need the anectodotl evidense you are asking for, ebia. We already know what will happen.
Like connecting the dots. Or filling in the blanks. We already know what the answer is.
We're adults. We know this stuff. It's not rocket science.
A minority will abuse it, yes. Leaving the majority without shelter isn't acceptable, so what's the alternative? The people running these places will take reasonable steps to minimize the abuse and that's all you can do.
Then why don't we allow co-ed housing?
Because that would make matters worse.