In Gaza, any massive and very bloody attack on the Palestinians would have to be weighed against the consequences of a massive and very bloody attack against the Israeli settlers in Gaza.
In the future, that will no longer be a concern.
Gaza move is clearly not military - it is political. As the matter of fact, many in IDF were against moving out of Gaza, because they will not be able to monitor Pals acquisition of more sophisticated weapons - anti-aircraft missiles, Katyusha rockets, etc.. With Israel out it would be up to Egypt to control flow of weapons via tunnels. I am not sure who is going to control port of Gaza, but clearly it would be open to all kind of abuse.
If "many" in the IDF were against it, that means that the others in the IDF are not against it.
Military strategy, like all other human endeavors, will have opposing viewpoints. Military history is filled with such arguments between respected military leaders.
My military opinion, as a third party unencumbered by any Israeli emotional considerations such as considering a defensive line as "hiding", happens to agree with Sharon's military opinion.
If you disagree with that decision, that does not make that decision "political" rather than "military". It only makes it different.
As an "occupying power", Israel's hands are tied in the degree of punitive force it can now unleash against the Palestinians. It just doesn't look good on the World stage when you flatten a city you posses "occupying power" over.
In the future, attacks by a Palestinian sovereign state can be met with overwhelming force by the Israeli sovereign state.
If the Port of Gaza becomes a problem by importing weapons used against Israel, the Israeli Air Force can flatten it and the Israeli Navy can blockade it.
In regards to anti-aircraft missiles, Israel is just as capable as the U.S. of defeating an anti-aircraft system. Arab anti-aircraft systems were merely a bump on the road in the Six Day War, the Yom Kippur War, the Gulf War and the Iraq War.
You view a Palestinian state as a means by which the Palestinians can acquire better weapons.
I view a Palestinian state as an entity which Israel can direct massive retaliation against in case of attack without being encumbered by all the political considerations it must deal with as an "occupying power".