It is not so much a matter of blame but of responsibility and caring for your brothers. At the same time about the same number of Jews were expelled from Arab countries and their property and assets confiscated by those governments. Isral could have shoved them all into refugee camps to extort sympathy and demand UN support, but it didn't. These people were absorbed into Israeli society (many iving in tent camps for over a year until appropriate housing could be built at breakneck speed), got jobs, and started building lives for themselves. So instead of blaming the Arab countries for this travesty of justice, Israel took responsibility for these refugees and gave them the opportunity of helping to develop the country for the benefit of all. And to remind you, Israel was no Rockefeller at the time - very limited resources (apropo yoour argument about Lebanon being a poor country). Can you see the difference?
Palestinian youths throw stones at security forces in Shoafat, E. Jerusalem; none injured (Haaretz)
from the article: Between prisoners and captives