Er... for starters, hasn't one of the biggest arguments against desalination been the ecological impact? Or are we assuming spherical cows here?

Yes, but that's localized and temporary. It's nothing like the ecological impact of burning fossil fuels, and more like the ecological impact of a quarry. It's a lower impact than a hydro dam, I think.

You have an intake that can suck in sea life accidentally, and an outlet that emits water too salty for sea life to survive, which doesn't go beyond a certain distance as it mixes again with normal ocean water.