Every country has its hot-heads, including Israel, so though Hamas seems to be a bunch of ruthless rednecks, they will always have people within their ranks who want to challenge any tendency for Hamas to cool things a bit - with rockets if necessary. That's people for you! The IRA had plenty of those too, ready to oppose anything which would curb their aggression.
UN: Gaza could be 'uninhabitable' by 2020 if trends continue (AP)
from the article: What Hamas is really afraid of