They don't have another country to go back to.
Actually, Palastenians don't ask Israelis to go back. They ask for their own right to return to the Israeli heartland from the refugee camps in which they live currently. Israel doesn't want to grant them the right to return, because then Jews will become a demographic minority and Israel cannot survive as a Jewish state.
In a sense, Israel is similar to the apartheid South Africa.
In my opinion, a just solution is to have a secular republic of Israel & Palastine with universal adult franchise. However, Palastenians and Israelis have to build up a lot of trust and mutual respect for that to happen.
As long as Arab nations stand divided, they cannot have a strong enough diplomatic/military voice to demand the rights of Palastenians. Israeli aggression in Palastine or Lebanon was just waiting to happen.
Where were the military bunkers ? Where were the bomb-shelters ? Where was the trade offensive against Israel ? Palastenians were just standing naked in front of Israel. Who should be blamed for this ?