As far as I can tell the Icon of the Seas is basically fine; even on the environmental front (important!) I see no reason to believe it's worse per passenger than other ships.

A lot of opposition to it feels like elite snobbery against middle / upper-middle-class people.

Any good anti-Icon arguments I'm missing?

Nothing I’m reading suggests it’s ’basically fine’ on the environmental front? I suppose if people are choosing this over taking a long flight somewhere , AND they don’t need to take a flight to or from the boat … maybe by comparison it’s greener?