Israel has been targeted time and time again in it's history by Arab Countries. Six-Day War, Yom Kippur War. It is justified to have such Arsenal in order to deter these states from using aggressive tactics in order to get rid of Israel. Back in that time , Arab Leaders aimed to drive the Jews into the Sea.
Yes, but you have to consider why this is the case, Palestinians don't hate Israelis for no reason, it is because, in their eyes, the land which is now Israel should, in fact, be Palestine. Now, I'm sure you can read up and understand the history - but the current situation is (like KingPomba pointed out) that both the Palestinians and Israelis call one place home and hence are fighting over that, both happenned to be born there and both have to put up with or fight over this situation.
It doesn't mean that the Arabs are right and the Israelis are wrong, neither does it mean the Israelis are right and the Arabs are wrong, they are both right and wrong and both are, to a certain degree, responsible for what has happenned - you can't just blame everything on the Arabs, you have to understand that, like Israel, they have a cause as well and they are acting the way they are for a reason.