Heck, I don't know -- whole families being traumatized? Children having their lives upended, because their parents suddenly have to move across the state (or the country)? That sort of thing? So you can live within walking distance of that fancy new Belgian beer bar, and your favorite S&M club?
It's one thing to acknowledge that displacement of existing (generally lowest income tier) residents is very unfortunate -- and yes, causes real suffering -- but to maintain that the cure (e.g. rent control) may be worse than disease. That's at least a position with a certain logic to it.
But what people reasonably resent about the new tech elite is that (some of them) don't even pretend to rely on sober assessments like the above. They just come right and out say it: "What's wrong with poor people being displaced? What's wrong with a city that school teachers, first responders, restaurant workers can't afford to live in? I'm doing fine -- why should I give a fuck?"