I think there's three main reactions to watching MLP:FiM.
First, full blown addiction. This is pretty much the bronies. Once you've watched your 4th episode, the likelihood of you joining this category skyrockets, and you may well be hooked in 10 seconds flat.
Second, mild disinterest. You watch it. It's not bad, but you don't see what the fuss is about, and carry on with your everyday life unchanged.
Finally, hatred. This is generally for people who have so absorbed media messages that they do not understand how an audience outside of a show's target demographic, especially one so different, can like the show, and actively go out of their way to troll and attack people in the first category.