The sale of motorcycles should be more restricted due to their excessive air pollution. People should be encouraged to use vehicles that do not excessively pollute the air. Motorcycles should be made difficult to sell or buy because they are an unnecessary mode of transportation and should be limited in the number of sales that are available.
Motorcycles should be restricted because of their excessive air pollution and also their excessive noise pollution. They can be make cleaner and quieter, so they should be. Why should other people have to suffer bad air and loss of peace and quiet just because some overgrown children want to call attention to themselves. "Look what a tough guy I am! I'm noisy and I make a lot of exhaust!" Grow up.
While motorcycles produce air pollution so do almost every other vehicle on the road and I don't think it's fair to limit the sale of one type and not the others, I think we are better off by developing vehicles that give off less emissions and make them affordable enough to be widely adapted.
Due to the size of automobiles, emission control devices can be included without influencing the vehicle's performance too negatively. Motorcycles, however, are small - too small, in fact, to effectively add many of the emisions-related components seen in cars. While research is performed in the area of motorcycle emissions, it is far more difficult to curtail those emissions from an engineering standpoint. Put simply, current science does not allow for controling emisions from motorcycles.
Limiting sales of motorcycles would not effectively reduce the problem, as motorcycles are already limited by weather and by personal preference. Motorcycles only account for a fraction of 1% of vehicle usage. Just because something is not necessary, that does not mean that it should be banned. At least in America, we have a right to liberty - the freedom to choose for ourselves. If we want motorcycles, we should be able to buy them without restriction. Low-emission fuel-efficient cars are already tax-incentivized.
I don't think that motorcycles should be restricted however I believe the way that we make them should be changed. We are trying to change cars, vans, and trucks for the better and stop air pollution and more eco friendly. We need to take this approach with motorcycles as well, and all things will work out.