It only takes a few thousand to make a difference.
Al Qaeda's audience isn't the masses: it's the unemployed, disaffected, idealistic young man who wants to throw his heart (and life) into a cause bigger than himself. [link|http://en.wikipedia.org/wiki/Sayyid_Qutb|Sayyid Qutb]'s ideas already have resonance with such people. If Egypt invaded Gaza to crush Hamas, you can bet that Osama and his acolytes would point to Egypt and say:
You see! This is proof that the Egyptians are [link|http://en.wikipedia.org/wiki/Jahiliyyah|Jahiliyyah] and they are attacking the true Muslim's! [link|http://en.wikipedia.org/wiki/Takfir|Takfir!]. We must protect the [link|http://en.wikipedia.org/wiki/Ummah|Ummah]! It's your duty as a Muslim to go to Gaza or Egypt to fight them!
I'm sure that more than a few would be susceptible to such exhortations.
If Egypt cracks down, they're damned by the press, in global public opinion, and feed the islamist arguments. If they don't crack down, they look weak and make it easier for those who intend to overthrow them by force.
In short, I don't think Egypt would move into Gaza unless they felt they had no other choice. If it gets that bad, all bets are off.
have you seen any restive outcry over hamas killing fatah?
Yes, in the reports I've heard on NPR. Remember the [link|http://english.people.com.cn/200706/13/eng20070613_383893.html|demonstration] a day or so ago of Palestinians demanding that the fighting stop? In other stories, many of the Hamas members/supporters were saying that the Fatah people were [link|http://en.wikipedia.org/wiki/Kafir|Kafir] - they weren't "true" Muslims. It's straight out of Qutb - I don't think most Gazans look forward to an islamist government and living under Sharia.
An unfettered Hamas government in Gaza could could cause lots of mischief in Egypt and other neighboring states.
Cheers,
Scott.