The real problem with this comic is that the “grow up” is coming from the left and the outright rejection is coming from the right. It should be the other way around.
As a conservative brony I must say that I actually know a few conservative bronies in real life, they are not totally uncommon. Granted, I go to a Christian college so that might be a part of it. My highly conservative family never got on to me about being a brony though, and I never had to hide it. The brony community does feel kind of liberal sometimes though, but I just try to avoid mixing my ponies and politics.