I'm not sure how this argues what I was saying but yeah, you make a good point.Now here is a thought which I admit probably is not the intention of the writers: The Ultimate X-Men are actually by definition terrorists. They are pure terrorists.
The reason is that there is a continuum as the saying goes that one man's terrorist is another man's freedom fighter. The difference is, even from the perspective of the US, the Ultimate X-Men have no constituency, no base among the population to speak of.
Just looking at US history, whether it was the Revolutionary War as fought in the South or the Civil War with groups such as Quantrill's Raiders, there is some group of associated people who provide support and safe havens. That does not appear to be happening with the Ultimate X-Men. They are basically alone. Now because of their superpowers they are enabled to be a lot more self-sufficient that how a random group of people would be, but that just makes them pure terrorists as would be portrayed in more jingoistic fiction.