Agreed. That is no different in my mind than someone saying "if Putin really wanted to succeed he'd..." people should be able to speak in favor of anyone and any activity they want especially if it's counter to government interests and/or agendas. Even if we are at war with the commies you are entitled to think we are on the wrong side of the dispute and advocate the other side convince enough people and the dispute may end with a meeting of minds and reduce overall bloodshed.
I don't know that I'd call giving someone a plane ticket far over the line either. Let's take the terrorist buzzword out of there. Then you just have someone facilitating travel to territory controlled by someone who isn't currently friendly with our government. If you want to buy your brother a ticket to Cuba because he really believes in communism I don't buy that you should go to prison for it. If he chooses to enter the military and is part of the Cuban missile crisis round two... well that is on HIM. And really, that is giving the whole thing too much credit. Cuba is a nation, capable of threatening hundreds of thousands if not millions of Americans whereas ISIS is merely a relatively new criminal organization that has yet to do as much damage to our nation as the disorganized Somali pirates.
Now, if you knew of actual criminal plans and provided the plane ticket to help them execute them that'd be different. That would be no different than being the driver of the get away vehicle in a bank robbery and if ISIS were not merely a criminal organization but an actual government we could be at war with like Cuba then I suppose the equivalent would be driving a boat to help them paint a target in miami or providing a plane ticket for the same that would be high treason.