In fact, a couple of months ago, I posted something similar (but far more succinct) about these two words.
Out in the field, these two terms are NOT interchangeable. The Left really does gravitate to the word "environmentalist" while those on the Right consistently describe themselves as "conservationists."
It may sound funny, but whenever I hear fellow biology/wildlife field workers describe themselves as conservationists, I know I'm in good company.
I know the "code." :^)