This isn't a matter of pro-military vs anti-military. This is a matter of ensuring the economic stability of the people. The United States of America has the highest military budget in the world, costing many American tax dollars.
Many empires have fallen from having the same policies as us, they set high military budgets and they are expanded globally and then they fall. Those who do not learn from history are doomed to repeat it.
This petition isn't asking for an immediate extraction, but for a very slow extraction. This will allow the nations who are used to American protection to start slowly warming their way to the idea and allows them to slowly readjust their budgets accordingly.
We must pull out before we are forced out as history will ensure our demise.