I like ranting!!!
Though thats not the only reason.
There is no better feeling for some people, then knowing they single handidly possess the power to crush somebody else's motivation. To some that is an INCREDIBLE power.
Why do people go into the genre they don't like and vote 0? Not because they sincerely don't like the genre, simply because that genre does not effect their lives, they choose to destroy that genres populace, to crush the hopes and inspiration to those who dwell in that genre, to subconsiously build their own.
After all, why would a heavy rock listener, give a DAMN if they went into techno or classical and just voted 0 on everything they saw? Does it effect their music? No. Not directly. Does it effect the person, to some, greatly so.
It is difficult to listen and appreciate many forms of music, because your brain grows up and thrives on one type of music as you mature. Think about it, a heavy rock listener would punch your lights out if you made them listen to classic, and a classic listener, would look at you strange if you showed them heavy rock.
I could give you a PhD thesis on this subject, but i'm going to stop here, i'm sure 75% of you stopped reading three paragraphs ago :).