So, if an American went to Vietnam in the 70's, put on VC clothing, grabbed an AK-47, lived with their troops and then took on combat missions against us we should arrest him and bring him back to the U.S.A. for a fair trail?
Thing is, you don't even have to go those extremes to be deemed "suspicious" or be red flagged as a "potential terrorist". You can just be a returning veteran. You can be someone who talks about the Constitution a lot, you can own certain literature, be a Fundamentalist Christian, etc, etc. All of the above have now been reason enough to deem a person a potential terrorist threat.
Ever notice that there have always been terrorists? That the WTC had already been attacked before? And short of some kind of Pearl Harbor-type event, it would have been difficult to get people to go along with all these executive powers the government has claimed and used over the past decade.
That's what this perpetual "War on Terror" has brought us. That even though it's ALWAYS existed, we only now, just recently in our history, have an ever present invisible enemy, that can be anyone, anywhere. And that's all the reason we need. The only thing needed to justify an action involving that is a press conference with the word "terrorist" said. When it became okay and accepted to do whatever it takes to "stop terrorism", we already lost that war, and that's IF it's even really being fought for that reason in the first place.
Like TSD said, it's the precedent being set, the precedents that have already been set, that should be what people are looking at in this.