Any American who supports Israel has the right to establish a land that "God gave them" should really think.....
Anyone who uses "God" in whatever situation needs to think. No god.
because if people can just take back land that was "stolen" from them and because they "say so". I as a descendant of the original owners of the land will be first in line to take back what is mine. Care to "give back" your land to any of my relatives?
Why has no one taken up the cause for dispossessed Palestinian property owners, in an attempt to redress their legitimate claims? The big answer is that the Palestinians have been used as pawns by their Arab benefactors. The Syrians, the Saudis, and the Iranians don't want to make sure homeowners are compensated for the loss of their property (many fled, abandoning their homes and chose refugee camps instead). They want the Palestinians as a people kept in a state of flux, so they can keep demanding that Israel be dissolved.
However, you point out one of the major problems with any questions regarding 'peoples' and lost land.
The only argument that could be used against 'me' and 'my land' would be that 'your' ancestors once held the land. It is an argument based on ancestral claims. The only argument more specious than this is the theological argument. It replaces what some imaginary god supposedly desires, with a grievance of long-dead persons. Admittedly, slightly more legitimate, but fraught with just as many problems.
Iraq used this excuse to invade and occupy Kuwait. The Argentine junta used it to invade and occupy the Falkland Islands. China uses it in their continuing occupation of Tibet. Germany had used it against Poland. It goes on and on. There is no easy way to settle such disputes because they use ancestral claims balanced against actual living people who (in some cases) have lived in the disputed area for generations. There is no easy answer, and in almost all cases with which I'm aware, the only way such claims are addressed is through bloodshed, with the winner settling the claim.
Let's take the cases of the Falklands and Kuwait. The Kuwaitis don't consider themselves Iraqi, and the inhabitants of the Falklands were British, not Argentinian. Forget the nations' claims: The people there did not want to be 'returned' to what they saw as foreign rule. Both arguments were settled by force. Kuwait was denied to Iraq, and the Falklands still remain free of Argentina.
Now on to Israel and Palestine
Dispossessing people of their land is generally frowned on in the 21st century. Ancestral claims and the even more tenuous religious claims are generally rejected in favor of the claims of current inhabitants to the lands in question. In light of this, the question of ownership of Israeli land (pre '67) is over. It was given to them and they kept it by force. Israel was founded, internationally recognized by the world's powers, admitted into the UN etc. Since this occurred over 60 years ago, most if not all of the original title holders to the lands are dead. If Palestinian sympathizers cared for the actual dispossessed owners, they should push for some sort of compensation for those remaining. Otherwise, this is a done deal. The children of the original owners have no rights to the land, and whatever compensation there is, should be adjudicated.
However, Israel seized land in 1967 in a preemptive war on the eve of a massive attack that was marshaled at their borders. They kept that land too long, and even now, are trying to hold onto 'Judea and Samaria' with the insidious Settlement Policy. This tactic should be roundly denounced. In fact, it has hurt American-Israeli relations, and in the long run, is dangerous for Israel and undermines the formation of a viable Palestinian state on the West Bank.