I think I agree with most everything that has been said, but I have two-cents burning a hole in my pocket.
This business of grass roots activism is not for everybody. Having been a volunteer for over a decade, and dealt with the same feelings about sporadic participation, I focus on my own reasons for participating:
First, it's the one small thing I can do to help keep access to our trails.
Second, being on the mountain gives me the opportunity to interact with other enthusiasts, face to face. When I talk to them, make the correlation of volunteering to address land use issues, I see a different attitude.
Third, the more people I meet with that common interest, the more I feel committed to the concept of influencing the culture of our community.
Fourth, my time spent observing, and interacting with enthusiasts give me a perspective I don't often see expressed. Last year I shared those observations, in writing, to support a grant application for the Clear Creek Ranger District to put extra seasonal employees on the ground.
Fifth, complaining about that one person, or group of enthusiasts won't fix anything, won't educate anyone, won't affect the overall culture of outdoor enthusiasts.
Like I said, it's not for everybody!
I do appreciate everyone who can make the time to volunteer, every little bit helps.