Should Vermont be allowed to secede?

There is a growing movement in Vermont called the Second Vermont Republic. It's an advocacy group pushing for Vermont to leave the union due to continued frustration over war, taxes, and an imperialist federal government. There is nothing in the constitution which expressely forbids a state to leave. However, that didn't stop the north from armed conflict with 11 southern states about a century and a half ago. But what about now? Do they have the right to form their own republic? Isn't the United States, after all, just that? A federation of quasi republics with independnet governements and laws?