There are people opting out -- there have been for many decades. It generally requires a group of people, though, at least one of whom can do something in exchange for government-issued money. Then the others within the group use barter or time sharing or other complementary currencies for what they need, in a mutually supportive fashion instead of a competitive one.

What makes an economy robust is not how MUCH money is in the system, but how fast that money moves around. So you can use anything else you want in place of government issued money, as long as the people agree to treat it as money, to keep the local economy going.