I think the argument about this one slogan reflects the whole situation with the marches. The intention perceived can be very different from that intended dependent on your view point and personal experience.
I think it does reflect the whole situation with the marches.
From the river to the sea is used by terrorists to call for the eradication of Israel. Some on the march actually want the eradication of Israel. There's a tendency to not actually blatantly call for the eradication of Israel in public because that looks bad, so call instead to 'end the occupation' or 'from the river to the sea', both of which are used by various groups and people meaning eradication of Israel.
And then you have the other ones, the ones who instead of going 'oh, those slogans are a bit dodgy, I'll avoid them', will use them and then argue that it's fine because they mean it in a different way.
And instead of going 'I don't want to offend anyone or be misinterpreted so I'll call for peace in a way that doesn't look like I could possibly want the eradication of Israel' I'll instead argue with people that they should know that even though others want the eradication of Israel, I'm not like that, and you should be able to tell that and not be worried about me even though I'm indistinguishable from the other lot.
It's just simple bloody-mindedness and self-righteousness to continue using slogans that rightly cause others concern and then to berate the people who get concerned and say it's their problem.