It's just American's anti-police, anti-government, anti-authority streak that cause them to rise up against it.
And there is a substantial view round the rest of the planet that America is a "massive and totally unaccountable police force" that it "violates people's rights left and right", as discussed here, for one example, when certain web sites get taken down and people who have never stepped foot in the USA suddenly have to be sent there to face American "justice", which Americans them selves seem most uncomfortable with.
Stones, glasshouses and all that.
No, it's called the principle of individual rights. The founding principle of the US, totally unique for its time. Now, it's mostly out the window, but it's still in our blood to some degree, as it should be. Also, limited government.
And not only does the TSA totally trample these American principles, but as others have pointed out, it's a much worse unaccountable police force than can be found in most other Western countries.
Remember, the TSA does not exist in isolation. By itself, maybe not a part of the road to tyranny. But look at the broader context (e.g., the government wiretapping everything, political parties that seem to be a complete farce, broken educational system, etc.).
The TSA shows that the government can and will arbitrarily inject itself anywhere in life, potentially under completely flimsy premises. As an American with a basic education in the history of our country, it seems just obvious to me that it was totally wrong for the government to ever have gotten involved with screening airline passengers. (I realize lots of people who know our history do not see it that way, though.) To me, this is very scary.
So again, it's not about the pat downs; that is not the cause, it's just the highly disgusting effect. People worried about TSA pat downs and scanners for their own sake are missing the boat.