That makes sense to me. At the same time I know the mediterranean sea is heating up more because it cannot move heat out quick enough. I dont know of any mediterranean air, so I believe more closed water zones would behave different than, lets say, the atlantic ocean.

Isn't it more akin in this case to worrying about too much carbon dioxide in the air?

Why is it akin to that? Doesn't the salt come from the sea in the first place?

A more apt comparison than you realize.

Most of the carbon we spew into the atmosphere came from the air. Ancient plants took it in via respiration.

That still doesn't make it a good comparison. The salt emitted by desalination plants is already in the sea now, it's not salt that went somewhere else.

And the water we take out eventually goes back.