Those meanings change over time, though!Historically, radicalism has referred exclusively to the "radical left", under the single category of far-left politics, rarely incorporating far-right politics though these may have revolutionary elements; the prominent exception is in the United States where some consider radicalism to include both political extremes of the radical left and the "radical right".
Yeah, like how 'terrorism' has changed over time from meaning 'violence against civilians to achieve military or political objectives' to include things like the use of violence against military personnel, both at home and in occupied territory, vandalism such as freeing caged animals, and the terrible crime of recording video. Terrorism has ceased to mean anything in the mainstream, it's become a synonym for 'something I dislike'. Much in the way that 'socialist' has been repeatedly used to describe the Obama administration, despite the fact that it is in no way socialist. Yet we can still use the real meaning of these words in intelligent discourse and discourage improper use.
I agree, and while I wouldn't describe the Tea Party as radicals, I think the author's point is that they aren't conservative by any traditional definition either. That's why they separate "traditional conservative" from Tea Party (that they then describe as "radical conservative). Maybe this is a case where a great word with a pre-established definition doesn't really exist.
The word you're looking for is reactionary. People, in conversation, may misuse words, invent new phrases to describe something they're thinking of, or even use words which mean the opposite of what they intended, but writers, public speakers, and people who wish to discuss things meaningfully should do better. It's really sad the way journalists will just parrot the PR that comes from political organizations and commercial interests, who are frequently misusing language deliberately to advance an agenda. Journalists are professional writers. They should know better.Maybe this is a case where a great word with a pre-established definition doesn't really exist.