Hamas may not be able to wipe Israel out (and I don't disagree with that statement), but that doesn't mean it doesn't want to. The destruction of the State of Israel is a basic tenent of what Hamas believes in - not neutralisation, diminishment or control - but its elimination. Also, whilst Hamas itself does not have the capability to inflict significant military damage on Israel, some of its allies do. Most notable amongst those likely to become engaged is Hezbollah (as opposed to Iran) and Hamas and Hezbollah are very different - the latter is far closer to a conventional army with much more advanced weaponry in much greater volumes.