I have have been to every place on your list except Brugge. For the rest I've been 2-10 times for all of them except St. Tropez (Louis de Funès' movies are awesome!).

I kind of see your point in this article, but kind of not. What does "ruined" mean? Sagrada Família is less pretty because there are non-locals there? Really? St. Charles bridge is ruined because of all the artists hawking? Do you think the bridge was empty 200 years ago? Same question for the Rialto bridge in Venice.

In all the places on your list, particularly Venice, I've found it extremely simple to get away from tourists relatively quickly and see locals, if that is what you want.

If there were no tourists in many of these places, then they would still be filled with locals, just as they have been for 100s of years. 6 of the 9 cities on your list have been major metropolitan cities for 100s of years.

Most tourists, like most people, don't have huge amounts of money and/or time. So when they can fly to the Netherlands they go to Amsterdam because they can do it in a day on a budget.

Taking the train down to Den Hague from Amsterdam (or to an even prettier city (IMO) that I won't name here) would take more time and money. Very much the same situation in Venice, Barcelona, Prague (a bit less), London, Brugge, Rome, Dubrovnik (a bit less) and definiely St. Tropez.