Hamas, no matter how many evil acts they commit, are merely a symptom of the wider issue that is both the expansion of the Israeli state and the oppression of Palestinians that have accompanied it. Despite signing some of these peace accords such as Oslo, Israel has still not ended the expansion of it's settlements despite resolution attempts, and this in part is down to the likes of Netanyahu who believe the land rightfully belongs to them. While we may not condone the actions of Hamas, and while it would indeed be preferable to see the back of them, can we still reasonably say that they are a surprise that came out of nowhere? Can we really be shocked that an extremist group would rise up in the wake of decades of Palestinian oppression? I don't think so personally.
I suppose where I disagree strongly is in the idea that Hamas themselves, as an organisation are merely a symptom. Hamas and the ideology they espouse are very much one of the causes. They're not just a group of angry blokes. They're an offshoot of the Muslim brotherhood and they are and always have been extremely well organised. They were set up with very clear goals enshrined in their charter ( the removal of all Jews from Israel being one).
I do agree fully that many Hamas members, in fact quite possibly a majority probably will have been driven to join the group as a result of Israeli actions. Bad behaviour from Israel and the subsequent radicalisation will have been a huge motivator for many to join the group and 'fight back'. So Israeli actions may well have caused /allowed Hamas to reach the scale it has achieved, but the organisation and it's vile beliefs would have existed and been pushing for violence even if Israel had acted perfectly. On top of that is also the fact that it's a bloody good career choice. Iranian funds have made being a Hamas commander or politician quite lucrative, all you have to do in return for your salary is ratchet up the tension.
The other side aswell: are Israelis allowed to have been radicalised by hamas actions? People a lot cleverer than me have written and spoken lots about Israeli society being pushed to the right as a result of the Hamas suicide bombing campaign.
It's a vicious circle. Israeli Atrocities are going to push more Palestinians towards terrorism. Atrocities by Palestinians push Israeli politics further to the right and increase the repression and atrocities from the Israeli side.
There are so many layers of trauma on both sides that I struggle to see how it can be attributed to one side being the 'root cause'.