I'm sure there are some people who make campaigning for "the right of return" a priority who have decent politics. But the majority of the political forces who make that demand central to their politics on Israel/Palestine don't; they do not believe that the Israeli-Jews should have national rights and see the collective resettlement of the Palestinians as a demographic way of undermining them. That's something I want to disassociate myself from which is why I don't use the demand.
I think it's also worth nothing that the politics of "the right of return" as outlined above also rather tend to let off the hook the Arab bourgeoisies who have been very much complicit in (and to some extent are responsible for) the miserable plight of the Palestinian refugees, who they have kept in poverty to use as a tool against Israel. Fighting for Palestinian refugees and their descendants to be allowed to return to Israel is fine, but we should also fight for them to have full civil rights in whichever country they've ended up in - something which the anti-Israeli brand of "right of return" politics implicitly dismisses.
I think workers in Israel should fight against immigration controls and for open borders. That's a different idea to "demanding" the collective resettlement of millions of people.
We're probably going to go round and round in circles here as we both apparently think each other's proposed programme for Israel/Palestine is utopian. For me, the geographical settlement that's reached is entirely secondary to the building of working-class unity. I advocate two states as a transitional demand because I believe it's the only demand around which such unity can be built in the here and now. I say, concretely, that Palestinian and Israeli workers should unite around a programme that recognises the national rights of both groups, up to and including seperate national entities if they wish. You say that they should unite around a programme that says "well, there might have to be some resettlement, maybe there'll be some displacement - who knows, really? Let's cross that bridge when we come to it." I think a programme that in actual fact says nothing concrete about the national rights of either group and is based instead on an abstract (rather than concrete) conception of workers' unity is the very definition of utopian.
On the stuff about rebuilding the left, I basically agree that reinvigorating the labour movement from the bottom-up is the primary task and prerequisite for everything else. However, I also think that a left shackled to what I see as essentially classless (or worse) politics on international questions will always be limited in what it's able to achieve, which is why I think debates like this are worthwhile and important.