I'm not a lawyer, and I hadn't really planned to represent my position in a debate, but I just want to point out a few things.
1. "US senators complain" is not the same as "illegal". Regrettably, in 2014 only the former is important.
2. The US has arrested non-Americans in many ways and on many occasions. I also point out that, instead of being arrested, "terrorist financiers" might just get killed via drone.
3. Even though the next 100 people may step up in line and continue the BTS-service offering, these people might be reluctant to do so. Moreover, they will have no reputation, may themselves be NSA employees, etc.
Again, I don't plan to run a full debate, the above points are very obvious to me. I anticipate some here to raise objections to which there are, again, obvious rebuttals. I don't really plan on pursuing the point, it was just something that crossed my mind, so if I don't respond please do not assume it is because I would have nothing to say.