Ah, I see, it's the same as "un-American", only without being a word too onerous to use (yet) due to obvious historical implications.
I'd heard of this but didn't realize it went on for decades.
Turning it around, I'd say persecuting political enemies for being "un-American" - or as a recent book declared, "unhuman" - is a very un-American thing to do. At least according to the values for which the nation stands (or supposed to stand).
Dude. Dude. You've said yourself: this Congress committee went on for almost four decades. And before it, it was Yellow Peril, or anti-Irish sentiments, or manifest destiny with its "the only good Indian is a dead Indian". So, no, it's a very American thing to do, has been since the foundation of the US and arguably from even before than that.