The tunnels are also the only thing that sustains their localised economy. I'm not defending HAMAS' use of them, but they also provide vital supplies to reach civilians. When Israel announces it's going to attack they give 3 mins notice. Gaza is under total blockade no entry or exit. Where do you expect the civies to go?
HAMAS stated goal isn't part of the political mainstream in Palestine. They are a fringe element that continue to be shunned by the civies due to the damage they've done, to both Israel, Palestine and its people and obviously no one in the international community deals with them in any official capacity. The PLO/PA has nothing in their charter that is remotely anti-Semitic, let alone anti-Israeli.