That's a generalization. By my understanding, Labor and Kadima accept that Palestine should exist as an independent state, and Likud do not. This would make Likud unreasonable, but Likud does not represent all Israelis, nor is it fair to equate support for Israel's defense and continued existence with support for Likud's policies in particular.

There are also Palestinian factions which are unreasonable, including Hamas. I think it's doubly unfortunate that both Hamas and Likud have managed to win various elections.