Travel isn’t the problem. There are plenty of lovely places on the planet so that all of us who are fortunate enough to be able to travel can do so, and in many cases, almost unnoticed.
The problem is that there are a small number of destinations which (a) real estate developers and tourism interests have decided to “hype” and which have become “in”, and/or (b) places which really are unique (Venice, for one). Simply put, we don’t spread ourselves out very much, either because we have put headline destinations like Venice on our bucket lists, OR we let the tourism agents tell us where the next cool place to go is, and we go there.
Obvously, if all global travelers, are trying to get to Santorini at the same time, there’s gonna be trouble. :-)
I would have no issue, and it may even be advisable, if certain of these “special venues” (Venice, again) were to start issuing their own “visitors visas” in limited and sustainable volumes. You want to go to Venice, and you’re not an Italian citizen? Fine. Apply for an entry permit and wait a few years, if you have to. This is not unusual for certain special experiences (you generally can’t get down INSIDE the Grand Canyon without a pass that you apply for months or even years in advance) and the revenue from the visas can be used to maintain the special tourist treasures held within.
(BTW, the secret to Venice is to hop the water taxi, and take it to a hotel or B&B on an out island, like Murano or Burano. Much cheaper, much reduced tourist activity, and then you can take the taxi to St. Mark’s or other places at your leisure.)