Oh please, give me a break.Geez.
Our nervous systems are evolved from those of echinoderms and fish, and those nervous systems could only evolve (in their current form!) in the presence of salted water.
Humans, a species noted for the evolution of the nervous system, could not have arisen without salt in the seas.
It's that straightforward.
Organisms as we know it require salt but only a very tiny amount.
There's significant salt in fresh water already, so getting the tiny amount of salt needed is not a real issue and evolution would help us to retain salt better if it were more rare. You know, like it does with potassium for example.
There's many ways that the world could wind up with much less salt without completely disrupting the existence of life, in fact the salt levels of the ocean have wildly fluctuated throughout prehistory.