See nothing about free speech
Sure there is - "
hostile attitudes toward its citizens, culture, government, institutions, or founding principles". How can you discover "hostile attitudes" if not through speech?
"Radical" speech is still speech.
Some threats are protected speech, other threats aren't.
and terrorist supporting foreigners.
One man's terrorist is another man's freedom fighter. See, for instance, the back-and-forth US relationship with various Islamic mujahideen groups. Or specific individuals, like the current president of Syria (Ahmed al-Sharaa).
The US has laws preventing material support for foreign terrorist organisations. However, there is a huge gulf between voicing support for a group like Hamas, and even for their terrorism, and actually providing support to them.
Do want radicals, threatening people and terrorists supporters here?
I don't want anyone threatening anybody. Anywhere.
However, I think that the US Constitution provides legal protections to speech that can be interpreted as radical, threatening or supporting of terrorism. And, I don't think that the wording of the Constitution limits that protection to US citizens. Rather, it tells the government what it can and cannot limit.
For instance. There are people out there who publicly advocate for homosexuals to be lined up and shot in the back of the head, because they believe that's God's will. I think they are radical terrorists who are threatening people. And, I don't want them threatening people and I don't agree with their speech.
But, the US Constitution protects their right to say it.