If we keep all of the territories Arabs become the majority west of the Jordan in short order. How can we remain a Jewish state and a democracy if we have to incorporate these Arabs into our population? Simply, we can't. This is why the Palestinians started talking about a "one state solution". We can never permit that to happen.
Gaza is a crowded, poor, desolate hole. We tried to give it to Egypt. They didn't want it back. We tried to give it to Jordan. They don't want it either. Nobody does. It is ungovernable and unmanageable.
What Israel needs is secure borders and safety for its citizens. We take away the easy targets for the terrorists and wall them in with the most sophisticated barrier known to man. If the attack from within their walls the IAF can respond without fear of killing any Jews.
Security and demographics both argue for disengagement. If it also, as a side benefit, improves our standing in the world and makes the Palestinians look like barbarians, that is all for the good.
Why the national religious movement enjoys so much support from the American right, and why the American right seems to want Israel to hold onto Gaza at all costs, is totally beyond me.