Okay, what do you think it means?
Since currently, it’s officially used by Hamas to call to genocide Israel.
It means that Israel should stop committing war crimes. Specifically that Palestinians should be free, and not caged, oppressed and in perpetual fear for their lives in the geographic area which lies between the Jordan and the Mediterranean. The subject of the phrase is Palestinians; Israelis aren’t mentioned, let alone Jews. It’s not about oppression for your group, it’s about freedom for another. This is evidenced by the complete lack of references to Jews or genocide in the phrase itself. It’s very, very basic reading comprehension without any mental gymnastics necessary.
https://www.adl.org/resources/backgrounder/slogan-river-sea-palestine-will-be-free
https://apnews.com/article/river-sea-israel-gaza-hamas-protests-d7abbd756f481fe50b6fa5c0b907cd49
You originally said
It would entail people of more than one religion living together and sharing a nation as equals. The horror!
So tell me. How does “From the river to the sea”, which is followed in the same sentences as rejection of zionists, somehow entail people of more than one religion living together? Even though they already do in Israel, which allows other religions, as opposed to Palestine, where belief in different religions equals the death penalty.
Regardless, it is a call to genocide and antisemitic hate speech no matter which way you try to justify it—final warning as to the rules: hate speech is not allowed.