Many Palestinians believe that violent resistance is the best way to get concessions from Israel. Many Palestinians believe that Israel cannot be trusted to hold up her end of any peace accord. Many Palestinians are open to extreme or moderate ideologies.
Right now, Palestine is split: recalcitrant Hamas rules the Gaza Strip, while the generally nonviolent Fatah governs the West Bank. Hamas has been actively Israel, but the West Bank has been almost completely out of the news, despite their greater access to Israel and Israeli settlers.
So how does Israel reward Fatah's good behavior? By allowing the settlements to expand, of course. More land is seized from Palestinian olive-growers and goatherds by Israeli suburbanites. The Israeli military continues to protect the settlers and wink at most of the new construction, even though much of it lacks permits. Agreements to close down illegal settlements and cease construction in specific places have been ignored, by Sharon's government, by Olmert's government, and now by Netanyahu's government.
This isn't to say that the Palestinians don't tolerate and even promote a lot of violence and extremism on their side. But when an easing of Palestinian resistance is rewarded with more land seizures and settlement, who can blame a rational Palestinian for joining the violent resistance?