gotta call complete bull**** on that... Being an active climber and sledder the amount of trash left behind by snowmobilers is staggering compared to climbers. Sure climbers aren't without fault but I pulled 2 packs full of crap off the S side both last year and this year after my machine took a crap. Oil cans full of fuel, beer cans, foil, food containers of every sort, plastic parts, clothing, Jaegermeister empties, more beer cans, etc. You name it, it was there on the snow. Hood Hill and Peanut knob were particularly bad... I was fairly disgusted. I like beer as much as the next guy but its inexcusable not to carry your trash out, it made it in...
Climbers leave wands (it's questionable when those become trash), the occasional rope, a sledom wind swept tent fly, and when an epic/rescue occurs perhaps more of their pack. If you don't believe me, hike up to the camps on the base of the Coleman or Boulder glaciers and see for yourself. There simply isn't much trash.
One of the most positive thing about us sledders is we (some) band together as a user group and take care of the messes. As climbers we can't even get along with each other, let alone other users, truly a band of misfits...
and not all climbers are "greenies"...