Unless the people in the region wanting secession are being oppressed or massacred more than people in the rest of the country, secession should not be tolerated.
The Revolutionary War was different because the Thirteen Colonies weren't part of Britain. They were colonies, and had every right to independence.
This is just the winners writing the history.
Had Britain won they'd have just said "The Thirteen Colonies were Colonies of the Crown and thus had no right to independence, as such their treasonous rebellion was put down."
You have a "right to independence" if you can enforce it, or you have someone else who will enforce it on your behalf.
Russia has helped ensure several small breakaway Republics in the Ex-Soviet sphere have de-facto independence even though the West does not recognize that "right".