Actually, believe it or not, it depends. Recycling can also be very bad for the enviornment. When you recycle paper, logging companies don't cut trees down, sounds good, except, when they do cut trees down, they plant more younger trees in there place. (you need to cut them down again in the future, right?). Since the logging industry isn't cutting down trees, some of them get old, and you get brushfires. Thats fewer trees, loss of homes and lives, and all sorts of air pollution. Its far more effective to let the logging cut down trees to produce paper, so that they can keep planting new ones.
Recycling plastics and aluminum falls into a different category in that it depends on how they are being recycled. In some cases, including one country in europe, they found they were creating more air pollution by trying to recycle then they would if they just burned it. You also get all sorts of waste if the recycling is not done efficiently and more pollution.
Recycling doesn't have to be bad, but that does not mean its always good.