Hamas does not tolerate any other organisation that could challenge its grip in power or put it in jeopardy by reckless actions (ie: provoke Israel over the edge). Hamas might be a dangerous organisation, but they are containable and predictable. To get rid off them in Gaza would open the doors to much, much more dangerous fanatics: Islamic Jihad and Al Qaeda. Unpredictable, suicidally fanatical and with a total disregard for human life, including their own. Those two in control of Gaza would pose a terrible challenge to the whole region. Israel, or even Egypt, could decide to erase Gaza off the face of the Earth, as the risk of an Al Qaeda run territory would be totally unacceptable to any party in the ME.
Yemen's vice president reportedly lands in Aden (Reuters)
from the article: PA arrests dozens of Hamas, Islamic Jihad militants in West Bank