Or, Dinner at the Kafka Cafe.
Check your political affiliation--
Are you a Republican, then no; well, maybe, but we'll let you off this time.
One of John McCain's top fundraisers paid 1.7 million dollars to a right-wing Colombian death squad. Woops. They did have to pay a fine. Poor things.
Not Republican? Then, quite possibly, Yes.
For example, here's the story of an Iraqi woman who has been denied refugee status because she paid ransom to a terrorist organization to free her kidnapped son. The ransom was the material support.
If your wife and children are kidnapped by a terrorist organization and are forced to carry water for them, then, tough. The water-carrying is "material support." There is no provision for duress.
Even if an organization isn't declared terrorist when you donate to it, if the US determines that it is at some time in the future, congrats! You're guilty!
"How should I reasonably have known of their activities before the U.S.?"Here's the law. Vague? Somewhat?