Even according to the Ramban, who holds that it is an official mitzvah, that does not mean an obligation like the obligation to put on tefillin every day. For if so, every Jew would have to do it and that would mean coming up en masse and taking control of the land, which is forbidden under the oath nowadays. Rather, it is an optional mitzvah. Today, individual Jews may live in Eretz Yisroel, but not as part of any organized effort to control the land.

Your central question seems to be: If a Jew living anywhere is in danger,
shouldnt he be given help? Isn't a Jew allowed to defend himself? Certainly if a Jew sees someone coming at him with a knife to kill him, he should pull out a gun and shoot the person first. But offensive wars are certainly prohibited. All the Israeli-Arab wars are considered offensive wars, because the Israelis are the ones who initiated hostilities by taking control of the land when they were forbidden to do so by G-d. The fact that the UN or the United States allowed them to have the land does not change G-ds law. Their occupation of the land is what precipitated all the Arab attacks. The Arabs are not motivated by anti-Semitism like the Germans. It could be that some of them became anti-Semitic because of what the Israelis did to them, but that was not the original reason for their anger. So: no, the Jewish people is not allowed during exile to put itself in control of Eretz Yisroel and then proceed to defend itself against those who dispute that control. We must relinquish that control and go live somewhere where we won't make anyone angry.