I've never been on a cruise, so it isn't something I've put much thought into. But I would definitely think that planes do much more damage overall and I hope that this pandemic will result in a lifestyle change and the realisation that holidays don't have to mean going abroad. There are lovely places to visit in this country.
I wouldn't want aeroplane travel to stop altogether, as lots of people have family overseas, but there do need to be big changes.
If the environmental damage from cruise ships are as bad as you're saying, then that needs to be looked at, too, but I can't help thinking that reducing air travel is the more urgent priority.
I don't think you've helped your cause by being so aggressive about this, though, OP, as there are also economic considerations. Also, in the middle of a pandemic, the majority of people have more immediate concerns.