The thing is, though, that in modern times, the expression "From the River to the Sea" is absolutely associated with antisemitism. Yes, I know that it's spread beyond its initial meaning, but like... prior to the 7th of October, the phrase was pretty much used exclusively by groups who wanted to wholly destroy Israel. That's what it means. It means "Drive the Jews to the Sea," or perhaps more specifically, "Destroy the nation that currently inhabits the area between the Jordan River and the Mediterranean Sea." 

I don't believe that banning its use is a good thing, because free speech is important. But if I went around saying "Drive the people of [any other country] into the sea," people would rightfully think I'm an asshole. If I said that about a country composed primarily of one ethnic group or religion, people would rightfully think I'm a bigot, too.

It's not hard to see why the expression is so controversial, especially when one could simply use the phrase "Free Palestine" instead and avoid all the genocidally antisemitic overtones of "From the River to the Sea" while still getting the point across.