BY1212, we certainly do own those places. How can you say we don’t? Even if we don’t control them (and for decades we did, so there’s no reason we can’t do it again) they’re still our property. They were our property throughout the years when various thieves and occupiers controlled them, and they will still be our property no matter who will control them in the future until Moshiach comes. The Arabs are squatters there, nothing more.
And the prohibition on giving away land from which it will be easier for the enemy to attack us, should they choose to do so, is an explicit and undisputed halacha in Shulchan Aruch, so those rabbis who held otherwise were wrong.
Every military expert agrees that giving these areas away will indeed make us more vulnerable. Even those who support it admit this, but say that the risk is worth taking for the sake of the promise of peace. If the Arabs are no longer our enemies, and decide not to attack us in the first place, then it won’t matter how vulnerable we are, and we’ll be safer than if we kept the land and they remained enemies.
But the halacha says explicitly that we are forbidden from taking this into account. We must make our calculation assuming that the enemy will attack, and consider whether control of this area will make a difference in that eventuality. If it will be of no use to them in an attack, then we may give it away (at least as far as Hilchos Pikuach Nefesh is concerned) but if it will be useful to them, as every serving military expert says it will, then we must not only not give it away but we must fight to keep it, even though fighting inherently involves risk to life. We cannot allow the country to be vulnerable to a potential attack, even from those who promise not to attack us.
Considerations of Kedushas Ho’oretz, Lo Sechoneim, and our lack of right to give away that which Hashem has given us, are all secondary, because they’re all subject to pikuach nefesh. (Except according to the Ramban, who holds that mitzvas kibush ho’oretz applies nowadays, and it’s obvious that that mitzvah overrides pikuach nefesh. This is why the zionist rabbonim oppose giving away land in all circumstances, even if pikuach nefesh demands otherwise. But the Lubavitcher Rebbe didn’t hold like the Ramban.)