Try hitting an after party for a pro contest-you'll see there's no shortage of pro bb's and amateurs abusing alcohol, coke, E, weed, Rx/injectable painkillers(Nubain), etc. I even know of a couple pros that smoke a couple packs of cigs a day. This doesn't make it healthy, or morally correct, but then again neither is AAS use.
Personally I think the sides from smoking weed are pretty tame when compared to the sides of the popular, more socially acceptable "happy meds" advertised on the 6 o clock news. If you think about it, most guys that can overcome the "dirty needle/junkie" stigma of injectable AAS use, is probably not going to have any fear of smoking weed or tooting up a line of blow.
Personally I prefer weed over alcohol because it doesn't have any calories and won't affect my workout the next day. Also, the munchies-thing is mind over matter. After you've smoked awhile weed can be used as an appetite suppressant when dieting as well. Weed + ECA = poor man's speedball.