1. Radical libertarian / anti-government types
2. Tea Partiers
3. The OWS movement
4. Anonymous
The moral of this story may just be that these groups have more in common that you would suspect at first blush.
And as far as I know, OWS was never associated with the Guy Fawkes mask; that was Anonymous showing up in the flesh.
Why does it seem silly to you that the largest and most effective anti-government movement of the modern era would have some sympathizers who adopt the symbol?
And to answer your question, because the Tea Party seemed to be all about being American and Fawkes was not only British but also Catholic. I guess pop culture helps.
The latter doesn't much look worth of downvoting to me, in fact I'd go almost so far as to say it's amongst the most vexing problems of humanity at the moment.
Yes, my point (such as it was) is that wedge issues distract from the real "supra-partisan" issues that affect citizens across party lines, like the immunity of bankers from prosecution, how much of a drain military expenditures are on the economy (and therefor quality of life) in the US, the TSA, US foreign policy as a stifle on travel opportunities, and so on.
Oh, but let's talk about some religious people laying a turd of morality on the front page of every newspaper. Birth-control in church insurance? Such a pressing issue!