Yes, snowmobiles should be banned in national parks. This ban would help keep the environment healthy, as that is the point of a national park. Any type of recreational vehicle will have lasting impact on the surrounding environment, through tracks on the ground or particles in the exhaust. It is important to protect the nation's wildlife, and keeping recreational vehicles such as snowmobiles out of the parks will be a good first step.
If we get rid of snowmobiles in the parks, then we should get rid of cars too. There are a lot more cars that travel through the park and pollute the air than sleds. Heck....Why stop there....Lets not allow any people in the park either, so nobody can enjoy it.....Lol.
Having been to Yellowstone National Park in the dead of winter, I do not believe it is a good idea to ban snowmobiles in national parks. From my experience, snow mobiles, were the only mode of transportation at that time, since all roads are covered in snow and closed. The national parks may need a more viable option invented before it could ban snow mobiles.