The most obvious example of this in context of travel are these huge cruise ships. No one is really doing anything wrong with that, as such, but craptons of tourists descending on your comparatively little city or town can become quite disruptive (as I've experienced first-hand as a resident).
There's quite a few problems like this, from small to large. Humans don't seem very good at taking "collective responsibility" for these sort of things, "because I'm doing nothing wrong", which is true, but also not.