Cruising to a destination is basically no different than traveling there by any other means, at least in terms of your impact on the local economy. Personally, if you're uncomfortable supporting the economy of a country or city for whatever reason, simply choose not to travel to that place. I would not have chosen to visit South Africa during apartheid regardless of how I got there, and I always chose to avoid Northern Ireland until after the peace accords in 1998. Those are choices we have to make for ourselves.