Why do you assume it has to be at someone else's expense? Venice was originally established over 1,500 years ago on a series of very low islands in the middle of a swampy lagoon at the north end of the Adriatic Sea. It is the lowest land anywhere nearby. Most of the rest of the Adriatic coast nearby has relatively higher land adjoining the sea. If they don't flood any more than usual, then this is not really a zero-sum game, is it?
If the oceans rise around the world you will likely see more of this type of initiative over the next century. There are similar solutions that have been implemented elsewhere already, such as the extensive dikes and land infills created in the Netherlands, the barriers around New Orleans and the Thames Barrier at Greenwich in London. Also, what about all the landfills that extended the island of Manhattan into New York harbor, or the waterfront of Toronto into Lake Ontario, and similar projects all over the world?
Just curious if you have ever been to Venice? It is IMO, one of the world's most beautiful and unique cities. It is also a UNESCO World Heritage Site. If you have visited, did you observe the expensive and repetitive damage caused by the constantly recurring
acqua alta? The barrier gates, like the ones on the Thames, are only raised as needed. The rest of the time they lower down to allow the centuries-old free flow of water and shipping.
I'm not sure I really understand the nature of your concern, nor what your suggested solution would be? Do nothing?