Horde doesn't always win BG's. Perhaps they always win the ones your in, but that does not mean that they win every BG. I play alot of BG's, and it seems to me that we win about 80% of them. I also keep hearing over and over again that ally's are young kids and horde are adults, maybe it seems that way to people due to the time they play. I play between 12:00am and 5am PST and the Ally's seem to act mature for the most part, but that may just because of the time i play. Also how does anyone know who is more mature when you are playing 1 faction at a time, there is no way of knowing if the horde have a bunch of immature players playing while you are playing ally, unless you have 2 comps, and are playing both factions. I think it is safe to say that both factions have equal numbers as far as mature players go, so you should pick the faction you want to play, according to your own likes and not because someone else has a harder time with 1 or the other.

My own opinion... i have played both horde and alliance and also feel that horde tend to appeal to an older group or more mature group and that the alliance TEND to be younger or less mature.  now thats not to say that horde doesnt have little kids running around or that no adults play on alliance, we are just talking about tendencies here.  since the beginning of warcraft, horde has been viewed more as the "bad guys" and alliance the good guys.  Kids natural tendency is to be the hero, the knight in shining armor, the good guys.  Makes you em feel good you know? (even though i feel the alliance good guys horde bad guys is a very flawed view.. it is the predominant stereotype we have in wow). I actually am the same way, except that i view horde as the good guys, thats why i play them.  Also i imagine as a parent, (this is a generalization, its not true for everyone) a good number of parents would rather their kids play as a human or an elf or something less grotesque then an orc or a zombie, and more human than a cow.  and i dont think there is anything wrong with that, i just imagine some parents lean that way.