in this case, it was a devil's advocate (since, again, I don't hold such a view). The purpose of the suggestion was to demonstrate that insulation is being done there, and nothing more. As for why a person with a legitimate reason besides trying to evaluate the group's behavior under a stimulus, I can only conjecture. Again, I don't hold such a position or view.
Some possibilities I have seen raised, may be that adults have more resources to expend on their fanaticism, and that the fallout of that resource expenditure can be very unwelcome; eg, "please remember that not everyone loves MLP, and some people really don't want to see pinky pie flying the tardis, M'kay?" And such. (That is an actual opinion expressed by a friend of mine. Much like The Doctor probably shouldn't go visit in places he shouldn't, Pinkie Pie probably should stay in pony land.) There is nothing really innately wrong with taking something you like and making tributes to it-- but in places of general assembly, like a public forum not dedicated to MLP, it probably isn't the best idea to expend lots of resources spreading pony propaganda. That could be a legitimate thing that they would like to address, especially after having been so accosted. (The other deviantart blog I mentioned but then couldn't find a link to was exactly about that-- MLP being crazily over-represented at DA, which is not a subforum for MLP fans. MLP can be there, but it probably shouldn't be epidemic, for the same reasons you just asserted above, and which I can agree with.)
If the community consensus is "MLP is WINNNN!", and this view goes uncontested, or such contestations are immediately maligned as "hating!", you end up with what happened on both of those DA blogs. This is because people that don't feel that MLP is win, will openly say so, and assert that they would like for you to stop. In this sense, "sex is fine and dandy, but rape is bad. Please stop raping-- adult MLP fans are more likely to perform intellectual rape on other genres, and I am opposed to that. If you would please stop that, I wouldn't have a problem."
That kind of thing is decidedly not trolling.
And yes, if the message is continually "MLP is GREAT!" At 100% volume to drown everything else out, then the only recourse left is to show up on the doorstep and let them know. That isn't trolling, it's self defense from the pink pony menace.
It's similar with nationalist propaganda. "America is #1", and "usa, usa!". As was said at the nuremburg trials, "tell a big enough lie often enough, everyone will believe it." More or less.
When every door is shut, and every means of being polite are excluded from you (because you aren't a pony fan, how dare you!), the only method left is to be impolite.
That's one of the reasons for things like Landoverbaptist and TheOnion. Both are decidedy trollish. Both are conveying a message about an insular group of people. (Religious fundies, who rail about "true christians', and the press, who rail about "real journalists'.)