I worked for a desalination company in the 1980s. From then until a few years ago, I would have disagreed with your assertion. Some recent advances have me rethinking that, however.
https://singularityhub.com/2019/06/18/inching-towards-abunda...
https://singularityhub.com/2019/06/18/inching-towards-abunda...
https://en.wikipedia.org/wiki/Sundrop_Farms#/media/File:1604...
It's a farm in the middle of the desert that gets all its water from desalinated sea water powered entirely by an array of mirrors.
However my past concerns for altering seawater on a planetwide scale are much abated. Rising sea levels and glacier melt have put an end to that.
Maybe I'm crazy or not informed enough, but I always thought this water-desalination thing was a solved problem. Then I got confused when they talked about how there is "brine waste" and it's a huge ecological problem. Why do they stop short of full evaporation of the brine?