first a few words about "colonisation". So ok, if it wasn't colonisation, how would you call it? it was a group of people who decided to live in a country that was already inhabited by another people and to take over (parts of) the land for themselves, (sometimes excluding the original inhabitants, but not necessarily). This is called colonisation, if you like it or not.
Can't you just for once imagine that your are a Palestine living in your country (which was occupied by another country, but that country, first Turkey, later GB, let the palestinians live there and didn't transplant its own population there, they just wanted tax revenues) . Than some people from outside decide to live in exactly the same city you do and completely controll this city by their own organisations, completely excluding the original inhabitants. Than there is war between your leaders and Israel and you flee. After the war you want to return home but you can't. You are not allowed back in and had to live in refugee camps.
I agree the rich Arab countries could have taken in the Palestinians, but Israel is rich too, why couldn't Israel take them back? It was where they belonged, not in Saoudi Arabia or Kouweit, but where their roots were, where their houses were, in short their homeland. The rich arab countries (who are indeed corrupted, etc. but that is beside the point in this discussion) didn't have to take them because they didn't live there, they lived in Israel, they were Palestinians belonging in what was Palestine, not Bedouins from the Arab desert, not even Libanese. Israel MUST take them back (UN-resolution), so in this case it is not anti-israel hysteria to ask for the return to where they came from, it is just common sence. By the way Israel's leaders already agreed to take all refugees back in 1948, on the condition that "peace-treaties were concluded". However, even after peace-treaties with the PLO, Jordan and Egypt, Israel still didn't take them back.
And about Arabs killing Arabs, it was true in many cases (by the way libanese killing Libanese, they are not just Arabs) but in this case it was Libanese killing palestinians under supervision and controll of Israel, which is a big difference.