The show was created for little girls AND THEIR PARENTS.  In other words, it wasn’t intended to only be enjoyed by small children, but to be loved by people outside of the traditional demographic, by people who cannot tolerate most programming INTENDED for only little girls.

Fans of the show, including bronies, enjoy it because of good writing, good animation, and wonderful characters.  Are these wonderful characters always kept as ‘pure and innocent’ as they should for a 'little girls’ show’?  No, but then again nothing that ever touches the internet is.  Believing that the show or the fandom has been destroyed because it has reached beyond the target demographic is incredibly close minded, and even sexist at times.  The show exists outside of the fandom, and though they may interact, the show does not need the fandom, and the fandom does not need the show.

As for the prevalence of pony porn that Junkie121 may be alluding to, yes there is a lot of it, but again welcome to the internet.  I can guarantee that there are worse things than pony porn on the internet, and within easy access of unmonitored and unrestricted children.  R34 is inseparable from the internet, and no matter what fandom you are in you will find it.  If you think that pony porn is bad, you are right under your opinion, but it is far from the worst thing that can be found.