>Why is it a problem when poor people want to move in but not rich people?

Because they are a drain on the local economy, often have mental and/or substance abuse issues, and live outside. Is that a real question? You can't honestly protray most homeless people as free spirits painting on the sidewalk and "living their best life".

Why is it a problem when a stranger breaks into your house and raids your fridge but not when you invite a close friend over for a meal?

Both are seeking what they think is a going to be a meal. Both are ever so slightly changing the character of their destination by showing up.

The programmers are raiding the housing supply. The homeless aren't.

Ok yeah you're right then. That makes it a fair comparison. I'll remember that when I see someone passed out in the subway with a needle in their arm as I walk by with my kids.