BBruce, now you're off on another tangent. Have I said Israel has no right to exist? And what does a right to exist mean? Human beings have a right to life, that I take for granted, even further than many people, as I count all the way back to conception. Do nations have a right to exist? That's an interesting philosophical question as it tries morally to equate nationhood with personhood which is altogether different. The former is a political construct of recent times, the latter a unique sentient human being which I won't even attempt to define here beyond that point or I'll get into another long ramble.
We generally accept the inviolability of sovereignty (well apart from Iraq let's say, irony intended) and that nations have a kind of civil right to pursue their course un-interfered with by outside influence or attack. In practice it rarely happens though I personally accept democratic nationhood to be a fair and just model of how things should be.
But a separate question is whether states that turn 'rogue' should be allowed to carry on their course without outside interference and whether states that are fundamentally flawed at heart should automatically have some kind of right to be whatever kind of state they wish, no matter how depraved.
By way of example we could think of Apartheid South Africa or Mugabe's Zimbabwe. The general principle has been to respect these nations' sovereignty and to apply pressure diplomatically and / or through economic sanctions. Under international laws and conventions as they stand regime-changing invasions have generally been frowned upon until the Bush camp decided literally to take the law into their own hands or disregard it altogether. The problem with this approach is obviously where do you stop? Zimbabwe would be a ripe candidate and a case could even be argued for invading Israel. But who would get to decide these things and how would we ensure it would be free of the stench of politicking and only enacted from noble humanitarianism?
No one has tried to argue that South Africa or Zimbabwe as states 'should not exist' but that's not the same as saying they should be allowed to continue as apartheid regimes or dictatorships without hindrance or comment.
I don't think anyone (and Lord help me if I'm wrong, rolling my eyes) here has suggested Israel should be 'destroyed' or the people who live there slaughtered, which seems to be what you're suggesting with your 'right to exist' phrase.
I hope this goes some way to answering your question.