Eh no. Oceans are big. Really big. Unbelievably big even. We're talking about filtering tiny fractions of ocean water, and nowhere close to all of it. Literally a drop in the ocean in comparison.
So, no. This is not a serious concern.
So, no. This is not a serious concern.
In absolute terms, we couldn't hope to remove enough salt from the oceans to be even so much as detectable in the absolute sense, but in local terms water with increased salinity can cause problems. Oceans are not hives of life everywhere you look, it's really just in spots, and those spots are generally right where we want to be and to put our desalization plants.
Plus the high-salt and normal ocean water are much more resistant to mixing than our intuition would suggest. They will eventually mix, but the high-salt water can go a surprisingly long way first.
Not going to be an issue with your average desalination plant, but certainly proves the point that water masses can behave differently in big, non-trivial ways due to their salinity.
I'm unsure on the impact of costs. Maybe we just pump it into the salton sea....
Every time there's a natural resource humans want to exploit, this is almost always been an argument, and it's almost always been wrong.
"look how many fishes are in the river! You can walk across the river by standing on the fishes!"
"Look how trees are in this forest! You can't see the end!"
Not to get all Derrick Jensen on this, but a red flag has been raised in my mind, as has my left eyebrow.