One problem here is you never know if a poster is an expat or a local, but even if all the contributors were US expats, I don't believe one could accurately say that just because some of the exchanges may be antagonistic, they evidence the existence of a trend towards polarization in the US. There are too few participants here to get any kind of reliable insight into trends in the US involving government, or anything else for that matter.
This is not to say that there isn't a trend towards polarization taking place in the US. Bad times tend to sharpen the political debate and you are living in a bad time in the US, probably the worst economic time since the 1930s. Even if the country isn't technically in a depression, people sure are feeling the pinch economically and emotionally. Now is a good time for ignorant and incompetent demagogues to seek impowerment.
If you are referring to the Tea party, I shutter to think what will happen if it gets much political power. Hopefully, it will only undermine the Republican party quest for control of the legislature, but I suspect it will have a gravitational pull on all of the issues pulling everything to the right (as that term is generally understood)...and they will be bad.
p.s. If you thought this thread evidenced vitriolic name calling, you should check out the threads on Israel and Israeli -Palestinian peace talks.