While I understand that it's technically right to detain if you think they're a terrorist or criminal, and if you had viewed online chats saying that they're going to, for example, make bombs, then you'd be perfectly correct to detain them for national security, I don't understand how it can be so misconscrued that a tweet between friends, where you claim to "destroy America" and "dig up Marilyn Monroe" can be taken as a serious threat.
Who else but government officials would think that two Brits travelling for a holiday, with little more than beer money, could "destroy America".
Will they detain all the silly kids who mention how they hate America online if they try to enter the country?
I'm also not entirely sure on how the American system works in regards to Terrorism Acts, but if they were detained as foreign nationals, are they not given a right to be met at an Embassy of their country?
I'm sure that it would be much easier for such a stupid predicament to be overcome with actual political ambassadors instead of questioning 2 holiday-makers over their rather obvious, if not stupid jokes?