Actually, from a psychological point of view, it is necessary for humans to catagorize people like we do. Often (possibly almost always), it ends in stereotypes, and/or bigotry, but it is still necessary for our brains to simplify basic characteristics, otherwise, we would never accomplish anything; we need to make quick judgements to move on to other things. On a side note, this "efficiency" only gets worse with age, which is why older folks are "set in there ways" and often criticize and judge books by their covers.... it still stinks.
I do all kinds of other stuff, but I still understand people catagorizing me as a "motorcyclist." I am. The thing that gets me is that much of the blanket images motorcyclists have were unjustly given to us by others, not our own actions.
In California, we share parking everywhere. I'll almost always leave enough room for another motorcyclist to park next to me. I'll also share a metered spot with a car, if I know there is plenty of room for the person I am sharing the space with to get out when he or she needs to, but I always make sure to add a little change to the meter too.
In San Francisco, there is a bit of motorcycle-only parking here and there (downtown). And (depending on where you are in the city) you can sometimes find parking on the sidewalk that is well out of the way of pedestrians. Out here, you will not find a meter-maid (oh, sorry, I mean "Parking Enforcement Officer") telling you to take up an entire spot of your own.
People are going to find comfort in sharing their distaste for motorcyclists, which is why there is such a strong voice in what they say. But look at the bright side: with the number of people buying motorcycles rising as quickly as it is, eventually the number of people who dislike/don't understand motorcycles will no longer outweigh the number of motorcyclists as exponentially as it does today.