Their explicit aim is the complete destruction of Israel. It is incredibly easy to believe. To quote the Hamas charter:

Israel will exist and will continue to exist until Islam will obliterate it, just as it obliterated others before it.

[Peace] initiatives, and so-called peaceful solutions and international conferences are in contradiction to the principles of the Islamic Resistance Movement… Those conferences are no more than a means to appoint the infidels as arbitrators in the lands of Islam… There is no solution for the Palestinian problem except by Jihad. Initiatives, proposals and international conferences are but a waste of time, an exercise in futility.

The Day of Judgment will not come about until Muslims fight Jews and kill them. Then, the Jews will hide behind rocks and trees, and the rocks and trees will cry out: 'O Moslem, there is a Jew hiding behind me, come and kill him."

Hamas is explicitly opposed to peace, and it’s sole aim is to murder or expel every Jew from the land. Any supporting these attacks needs to asked if this the aim they really want to support.