Its not really what the act is about, it is what it is leading too.
Well, call me when they get to what it is leading too and I will draft an amicus brief against the curtailing of liberty. I'm not particularly convinced by a slippery slope argument, I've worked with too many lawmakers. Change is slow and difficult and inefficient, and every little clause can lead to months (or years) of arguing. Maybe RICO lead to the Patriot Act. If so, those two are baby steps - especially if, as I believe, the exclusionary rule was made over broad by a series of decisions in the 60s and 70s.
People that try and compare the Patriot Act to the parable about "First the Nazi's came for the Jews, but I didn't complain because I wasn't a Jew... etc." miss the point that the Patriot Act doesn't come for anybody. It doesn't taget a people, it targets a type of actions that are, point in fact, already illegal, and then makes evidence gathered in trying to prevent those activities easier to admit in federal court. If it targeted a people, that would be a problem. If there are laws against Austrailians, that is a problem, Australians are Australian no matter what they do. Making laws against being a baker is different, because it is a pattern of behavior, and bakers can do something else.
In this case, the law is in regards to evidence admission related to a patterns of behavior advancing terrorism. Terrorism itself is not already legal. Keeping out evidence was always against the state's interest, because terrorism is an attack on the integrity of the state. It was passed by large margins the first time, and while slight alterations were made, a very similar version was also passed into permanent law in 2006. Why? Well maybe terrorism. Personally, I believe it passed the second time not becuase of 9-11 nostalgia, but because the people voting on it were themselves lawyers... and outside of the popular symbol it had become, as lawyers they all understood both why it was needed and that its provisions are not as pernacious as its critics claim.
I do not happen to support either major American political party, and am only registered to vote in the United Kingdom. I have never voted in a US election. However, as a lawyer, attacks on the Patriot Act frustrate me. People think it symbolizes something, but it is a misperception... and what it actually does is very sensible, which is why it has consistantly been supported by the American Legislative branch, no matter what its constituant members say to rally their supporters.