Well I'm not sure dirt bikes do as much damage (even off trail) as a lot of people assume. Yes they tear up the soil, but what do you do with a rototiller? Tear up the soil to promote new growth. It isn't only destruction (although of course yes, it can be damaging). Plus, they're probably doing less damage than the guy in Louisiana "rollin coal" in his "stacked" turbo diesel F350, that he commutes in by himself, and never tows anything with... Just saying, it's all about perspective. I'm all for avoiding truly unnecessary environmental damage. But you have to remember that just being alive and walking around on the Earth is technically causing damage. Not to mention all the paved roads we've built, all the forests cut down to build our millions of homes and factories, etc. Those things add up to a WHOLE LOT more than all the dirt bikes in the world times one million. Just saying... This being said, I can see where you're coming from and can certainly respect a different opinion, as long as you're not a rotten jerk about it like some people.
P.S. What was painful is hearing those 450's bounce off their ~11k RPM rev limiters ;-) That "hill climb of death" is so nerve wracking. I've been on some pretty gnarly ridge lines with drop offs similar to that and it never gets easier lol! I always think to myself "wtf are you doing" when I'm on them. But when you get down again it feels like you've gone to war and survived.