Currently it is a form of old-NascentAI-on-steroids: +3 RP, +2 IP, and +10 stability, all unfocused, but only if not terraformed. -10 stability if terraformed and no bonuses. And it does not apply to belts or GGs, so belt/GG-dwelling species can't be environmentalist, which is a bit odd but OK for me. It also gives a freaking -5 PP that is too much, equal to GGG or both Automation empire-wide flat bonuses, it restricts too much what to do with your planets or when to be able to adopt the policy (must wait until that -5 PP is not that much compared with your industry-focused planets output, and the rest can't be set to industry because they just give 0 PP).
I propose this:
Make it exclussive with Industrialism and change the -5 PP to -25% PP. So an Industrialist empire has 1.25*industry, an environmentalist empire has 0.75*industry, and the rest have 1.0*industry.
If non-terraformed:
+5 stability (it's nice to live on natural environments, but not has nice as to give it +10, you can die eaten by something when on a walk, and disposable envelops are forbidden which is a nuisance).
+0.2*pop RP research-focused (keeping great biodiversity is good for research, but only if you study it, Mother Nature won't serve the results on your desk on its own; better for fluff to leave the flat bonuses to stuff more related to infrastructure, AI, and automatization).
-25% influence upkeep (it's easier to maintain the society and economic system when it is based on natural way of life). Together with Isolationism this would be 0.375*base_upkeep (not 0.25).
+1 IP if stability > 15 (you keep people so happy and well attended that they get really loyal to you and help you carry out your deed).
-1*HabitableSize population if it does not make the planet uninhabitable (Environmentalism has a toll: leave more space to nature, less for the species).
-10 infrastructure (no changes here).
+10 planetary stealth (industry is blended with nature, being harder to detect).
if terraformed:
-5*(distance to original env.) stability.
Comments? Conflicts with other policies or techs that I'm overlooking?