It just opens up another front, and now Israel is completely surrounded on all sides. At least Israel could counterattack when the threat was land based, but what can Israel do but nuke the Mediterranean sea now?
That's why Israel maintains the by far most powerful army in the Middle east, and one of the most powerful in the world. Don't forget Israel was already gangbanged by 5 or more established Arab countries in an attempted genocide, immediately after its inception in 1948 and survived. Things only gotten better since then. No sane Arab country would get into a military conflict with Israel - look at how Syria behaved like puppies after the Israeli attack on their reactor.
But this also showcases the danger of false flag attacks and collective punishment, any terrorist group can trespass into Jordan, the West Bank, Gaza, Lebanon, Egypt, or use the Mediterranean sea to peg missiles into Israel without the knowledge or consent of any ruling bodies, and then when Israel retaliates, sooner or later they have no choice but to attack Israel in turn.
Full of BS, buddy. The biggest Muslim terror attacks ever did not even target Israel, and if AQ ever gets a nuclear weapon, it will sooner find its way to sleepy, liberal and impotent Western Europe than to Israel.
Now, neither Lebanon or Egypt will not allow any extremist group to operate against Israel from its territory, they crack down on them brutally. Just look at what happened to Hizballah operatives in Egypt lately. Hamas was dealt a good enough blow to lay low for the meanwhile - you don't hear of too many rockets now, do you - and the Palestinians in the West Bank don't want a Cast Lead #2 aimed at themselves, so they too keep quiet.
I'd say Israel has a very good handle on this situation. The only real danger is Hizballah, but not for the interests of Lebanon, but for those of Iran. However I guess that if following an attack in Iran, Hizballah opens a front against Israel, the IDF would be in no mood for assuring civilian safety like it did in 2006 and Southern Lebanon will burn, and personally I hope cleared of all inhabitants, demolished and annexed until a peace agreement between Lebanon and Israel takes place (might be 50 years for that).