Oohh, big words! Ethnic cleansing!
No, their displacement is Israel's responsibility. Of course it isn't "rendered irrelevant by time," it's rendered irrelevant by geopolitical necessity. But their living conditions, their rights, their political freedoms and way of life are completely and entirely the responsibility of the states which they live in. Herding them into camps for the sake of pressuring Israel is not ethical by any standard, and certainly worse than what Israel is doing in the West Bank. We don't persecute Syrian refugees to make Assad look bad for letting it happen.
There would be no 'Israel' if the Palestinians had remained. This is beyond dispute.
Let's grant you that ethnicity isn't as fuzzy and religiously-based as it is in the Jewish case. It still seems that Israel defining itself as a Jewish state isn't a whole lot different than Greece being a Hellenic state, or Finland being a Finnish state, especially given the fact that supposedly modern, liberal countries have ethnic conflicts to this day. I don't think it's a stretch to argue that most British people are of a "British" nationality, rather than being Scottish or Welsh or English, simply because they have so much in common with each other in addition to being politically united.
The allusion to race that Palestinian propagandists like to make fails utterly because Jewry, as a collective identity, can view themselves as simply one equal part of a greater whole. The problem is there are no such peoples left (the obvious candidate, the Samaritans, are virtually gone), but if they were still present some kind of political relationship could be established. Jews and Samaritans can find common ground, Jews and Arabs can't. It is extremely unlikely that they would ever view each other as being countrymen the way English and Welsh do each other. Ethnicity is a characteristic of Jewish nationalism, not because the Jewish faith or blood is considered the basis for that nationalism, but because of the fact that it is a self-contained civilization in Huntington's sense of the word.
When we expelled the Palestinians, it was because there was simply no way to accommodate them. We did leave those who were loyal to the state (and plenty who weren't), but it really should have been more thorough, in my opinion. It's the same for them; Arab ethnicity is the basis of their identity. The Arab armies expelled Jews from towns that they captured, and they were right to do it, because those Jews, simply because of their Jewish identity, would have aided the Zionists and sabotaged their enemy.
Morris argued that ethnic cleansing is justified, and I think it doesn't need an argument because of course ethnic cleansing is justified. When people are expelled for a reason that in any way relates to their background, mythology, or culture, that's ethnic cleansing. When the Allies kicked out millions of Germans from their homes during WWII, that was ethnic cleansing. I don't see Germans demanding a right of return.
There's a difference between kicking people out because you think that they are genetically different and kicking them out because, on the basis of that ethnicity, they are an insurmountable barrier to your own freedom.
I know it's easy to say, sitting on your computer in the most diverse state on Earth, that simply because someone has red hair or believe so-and-so about God is no reason to treat them differently. But when I go into the poorer neighborhoods, I see racially-based gangs and segregated neighborhoods. And that's normal. In Israel I see entire Jewish towns and Arab villages, and the interactions between them. People in every country in every part of the world live segregated. Those barriers will never be torn down, even if nationalism itself crumbles under a glorious communist revolution; Jews will not marry Muslims, Muslims will not marry Jews. The best we can do is learn to live among ourselves and tolerate each other's presence.
Sorry for rambling, I'm not feeling too motivated right now.
Arab birthrates are 1% higher than Jewish birthrates and the gap is closing. I've heard this demographic bomb nonsense peddled everywhere on the internet, but none of the proponents seems to have any argument beyond this.
Wow.

You have some shocking opinions here, but then again I live in the most diverse county in the most diverse state in the most diverse country on earth - so pardon me when I call you out on your claim that "Jews will not marry Muslims, Muslims will not marry Jews".
If that's the case where you live, then you guys are doing something wrong. Because that happens here, and there is no matter/antimatter asploshuns.