I was actually trying to discover whether there was sufficient reason to be cautious about identifying with the Black Watch tartan when I came across this site.
I hear this quite a bit from "neo-Jacobites" among the Scottish-American community, but it's really a "non-issue".

The Black Watch Regiment, and the other early Highland Regiments, allowed former Jacobites and other Scots to retain elements of their culture which the Proscription Act had banned. If it wasn't for them, we wouldn't be wearing the kilt today. The man who reportedly gave them their nickname, Lord Duncan Forbes of Culloden, was an active defender of all Highlanders, even though he was a government man. He stood up against the abuses of "Stinking Billy" Cumberland in the Highlands in Parliament.

As an American, I also have great respect for the Watch because their regimental history states that they took no Battle Honours from the Revolution because it was rightly believed that Battle Honours could not be granted from a war against "kith & kin". That is the epitome of gallantry.

The Black Watch have nothing to be ashamed about. Wear their tartan with pride!

Cheers,

Todd