America: Love it or Leave it!?

I've always hated this comeback, along with the similar "why don't you move to [insert communist country here]?", for many reasons. The obvious one is that it implies people shouldn't question authority or advocate for policies they want to see enacted; they should just grin and bear it. There are many other reasons, but can anyone give me a reason why this is a good comeback to use against a fellow citizen when they are voicing disapproval of a policy or advocating for a policy?