The monarchy had repeatedly violated the patriots (uncodified) constitutional rights, their common law rights, and their natural rights. The legal debate became the American Revolution, and America won. Furthermore, many of the sons of liberty had never signed or taken oaths of allegiance to the monarchy.
Some of them did take oaths of allegiance though, so you actually touch upon a very interesting subject that I think would be worth having a more nuanced conversation about. So thanks for spurring me to think further on the matter.
So far, the main thing I can think of is that part of the oaths of allegiance include duty, not just to the monarch but to the laws which create that monarch, therefor I find the view of the The European Court of Human Rights retrospectively insightful in that it ruled that the oath of allegiance to a reigning monarch is "reasonably viewed as an affirmation of loyalty to the constitutional principles which support... the workings of representative democracy in the respondent State."
Now, if you want to advocate against the constitution, as long as it is just speech, that is legal (as long as you are simply a citizen and haven't taken an oath), but I would agree it is treacherous, but not traitorous or treasonous. The second speech becomes action, particularly to assist a foreign entity in that venture though, it does become treason. I highly disagree with the sedition laws which violate the first amendment and have been so harshly abused even in the modern era, so I am ignoring those for the sake of conversation.
You said you "don't want to join any empire, but I would advocate for globalism, which I don't believe is the same thing as imperialism." I would simply say I think you are wrong and provably so on this point, in that the current trend of globalism is indeed an imperial globalism.
That being said, I will admit that I have often had the conversation about the utopic version of globalism, but it is important to differentiate between that imagined ideal which I think you might be referring to, and the reality of the current global geo-political movement of globalism (which is quite different from the economic fact of globalism, which I don't think is up for dispute).
If you want, I am willing to expand on the more technical reasons I think that current global is imperial globalism.
I wish I could edit my gp comment, because I was obviously wrong to say : "Of course, any American who advocates for such a thing is traitorous, "