It's pretty clear nothing is going to change your mind but you'll either pay it OR you'll stop cruising to places that charge it. You make that choice
If you disagree with this tax and the way it is implements finding an itinerary that does not have a port with that is totally up to you.
But to clear up things:
1) As far as the port it's things like crew members there, ropes and ties, gangways and if tendering that also comes into play to ensure that docking area is kept up and many more things. So you say you don't want a fee assessed by a local government in the form of a tax but you're okay with the cruise ship passing on in portion a parking fee by means of port taxes and fees charged? You're going to be paying that whether you get off the ship or not
so you're not really making much sense there.
2) There's ecological factors such as pollution, wildlife concerns, maybe you've heard of how strict New Zealand is with what organisms a ship carries with it into waters (they will bar a ship from entering their waters if you fail inspection), Norway is banning any ships from certain ports unless they are zero emissions. You just being on the ship is a contribution to these things. You staying on the ship is part of the problem too there because the ship is staying on the whole time...for your leisure
3) As far as limiting ships and sized indeed that is some things some places are doing around the world from either limiting size such as Venice (which now also has a day guest charge as well as an overnight guest charge for hotels and the like) where ships too large must dock outside the city (even the 600 passenger ship I was on last year was too large to dock in Venice but a Uniworld ship was able to). Amsterdam has moved their main port away from the city center. Alaska reviewed banning ships/capacity control, etc. Realistically Mexico has only a few key spots. Cozumel is probably one of the main ports.
I think it's pretty valid to be concerned about how much money is going to the local economies, because ultimately that's been the goal of many of these destinations that have done mitigations towards cruise ships, but your reasoning of not getting off the ship you're still part of the whole system whether you like it or not. Different places have different challenges they are trying to work with with respect to implementing mitigation strategies.
At the end of the day cruise elsewhere if this or any other method bothers you, unfortunately more and more places are adding these measures.