There's nothing wrong with liking anything that doesn't harm you or others, and what other people think of your interests doesn't matter in the long run anyway. On the other hoof, like Vukasin said, the mantra of "love and tolerate" is pretty much the golden rule of being a Brony but it's also simply being a fan of the MLP:FiM series and of its values. So on its face, being pro-violence wouldn't be part of said community. Perhaps if you clarified what you meant by that, it would help determine where you would stand as a Brony. Are you talking about stuff you'd see in rated R-films and involving blood and gore? Or are you talking about being violent in safe ways, such as two people yelling at each other as they whack each other with Nerf bats to simply let off steam? If it's the former, that would be very much against the Brony ideals, but the latter would be ok IMHO.
By the same token, there are a number of grim dark stories out there and those authors could be considered Bronies. You could also be pro-violent in one group setting having nothing to do with MLP, but love and tolerance in another that is MLP centric. And then I'm sure there could be a group of MLP fans that sometimes like to RP violent themes but are still generally good natured. So it also comes down to when and where you consider yourself a Brony, much like with being Furry. When I'm at work, or even just out and about, I'm simply "ME". I don't show my furry side unless it's warranted like at a meet or con, but that doesn't make me any less of a fur. You could say the same about being a Brony, so you could feasably consider yourself one even if the setting doesn't call for you to show it.
