It's not that this is an unpopular opinion, but rather that it's a dumb opinion. You're defining things one way and someone else can define them a different way. You can both define what an environmentalist is differently and that will affect the result of your question. If you're insisting that you own the definition of an "environmentalist" then you're being dumb.

In fact, I agree with the unstated premise of your statement. I think the risks of nuclear waste and a nuclear meltdown are much less than the risks of global warming and therefore nuclear power is good for the environment. However it is also a perfectly valid opinion that we should just reduce our energy usage and reduce global warming in that manner. I think it's unrealistic, but it's possible if we had the desire to do that as a collective. It is a valid opinion to be on that side of the fence. I think it's the less pragmatic approach, but I've known many people who are hippy environmentalists and it's still a valid position.