Being a loyal and dedicated fan of anything is a problem. Do you want to know why? Well, I’ll tell you why.
First, inevitably, none of your friends will be fans of the same thing. They’ll either look down on you because of your fandom, or they’ll just pity and ridicule you fondly for it every chance they get. Either way, you’re alone in this except for strangers you might meet and befriend through your fandom.
Second, you’ll waste money to no end. No matter what it is, be it merchandise or new music or tickets or rare items, you HAVE to have it. You just have to. Your world won’t be complete without every single artifact you can find that has to do with your fandom.
Third, you will be branded something extreme – emo, football freak, Trekkie – even if you’re relatively healthy and don’t spend all of your time on forums and at events.
Fourth and finally, society at large seems to find it amiss when we fans scream and yell and gather for some reason or other and often we will have a hard time fitting in if we don’t learn to curb our enthusiasm and find some topics of conversation that don’t have to do with our love.
Conclusion? It’s obvious, of course! Love nothing to the extreme and succumb to the mediocrity of society and of life! Then we’ll all be happy. In a mediocer way at least.
Slightly Ignorant 
I think it’s much more of a marketing thing. If we all like the same things- in moderation, then very few, very general marketing strategies will hit large swathes of the population. The other extreme is marketing personalized to each individual, taking into account every facet of the individual’s life and the degree to which they prioritize that facet over any other- essentially, no marketing at all, since too much control and decision-making power has been handed to the individual.
That’s definitely true, but the result of that marketing strategy is that annoying “mediumness” of everything.