Well, you could ask the poster in your local forum how he/she justifies the costs on nature and pollution caused, by his/her own internet browsing? Electricity does not appear out of nowhere... Not to mention the all the lands ruined by all the cables laid down. Put to that all the terrible chemicals used in computers..
Anyway, I have seen studies here in Sweden where the flora and fauna on the mx tracks are actually thriving, and the constant stir of the earth is actually providing a wonderful habitat for speices that are in trouble in our concrete industrial world.
Not saying one could ignore environmental effects, but we need to look at the grand scheme of things first. There are other more dire threats to the environment than a few dirt bikes in the desert.