What best completes this sentence?
Joe, in opposition to environment-friendly sentiments, has decided to go ____.
The best way to complete the sentence is to rewrite it. The only meaningful English word in common currency is anti-environmentalist, but using that simply exposes how trivial the sentence actually is in the first place.
Joe has decided not to endorse environment-friendly sentiments would be an acceptable rewrite. I think Joe has decided to become an anti-environmentalist sounds odd, but maybe that would do.
Sometimes the best way to describe the opposite of doing something is by not doing it.
If Joe is just not letting it factor into the equation, I would say this:
Joe, in opposition to environment-friendly sentiments, has decided not to go green.
If Joe is actively intending on choosing the most harmful products he can find, ...
Joe, in opposition to environment-friendly sentiments, has decided to go to Hell.
;-) Kidding, sort of. Although I don't have a way of saying that.
I would go with polluting, environmentally hostile (or unfriendly), antiëcological (or antiecological, or anti-ecological; see here).
As the context is already clear, why not a more general term? For example...
Joe, in opposition to environment-friendly sentiments, has decided to go to the opposite extreme.
A lot of answers which provide better style, but if you really wanted to complete THAT sentence, I think synthetic or extravagant might fit, depending on whether he's rebelling against the "natural" concept or "minimal waste" side of environmentalism.
Joe, in opposition to environment-friendly sentiments, has decided to be as unfriendly to the environment as he can, given his spiteful streak.
Environmentalists picked the color green as a descriptor because it is associated with nature and growing things (plants, trees, grass, etc.). Since you want a parallel structure, I would pick a color which invokes the opposite idea. I'd use black due to its connotations of death.
The urban dictionary, for example, has an entry for "black thumb" as an opposite for "green thumb." http://www.urbandictionary.com/define.php?term=black%20thumb
If you feel it's needed you could qualify the expression with an explanatory parenthesis.
Joe, in opposition to environment-friendly sentiments, has decided to go black.
or
Joe, in opposition to environment-friendly sentiments, has decided to go black (i.e. anti-environmentalist.)
I would say that you could say that he had gone right, in reference to those in right leaning political spectrum that rebels from the green movement. This is likely to be neither insulting nor incorrect.
neerg
orungreen
? :)