Well, I gave you a chance to back down and you didn't. So here we go: an extremist, by definition, is someone whose views are supported by nobody or a vast minority of people. Now, whether you agree with them or not, there is a substantial number of people in this country who do support animal rights and environmentalism. Rather than quibble about the exact number (you'll have your statistics and I'll have mine), it is definitely not a "vast minority". Therefore, simply being an environmentalist/animal rights activist doesn't make you an extremist, since you're not doing anything "extreme" in the American scope of views on the issue.
Of course, it also depends on what you call an "activist". Is an activist someone who votes for environmentally-friendly candidates? Or someone who makes a donation to PETA, or peacefully marches against the AWNR proposal? Or someone who murders people who don't share his views on animal rights? I think any reasonable person would call the last example an "extremist", but the other examples are safely in the "mainstream," even if it is in the Democratic "mainstream".
But going by your words, anyone who "takes action to promote any of these ideas" is an extremist, and that covers all of the examples above. Is it a common tactic of yours to call those who don't agree with you in any facet of your life an "extremist"? Maybe I should call my wife an "extremist" the next time we can't agree on where to go for dinner, and we'll see how far that gets me. =)
Voting for an environmentalist is simply an uninformed decision, it hardly constitutes activism.