I would hope not. There is no such thing as a "Catholics only" or "Jews only" thread, for example. Anyone here can post anywhere they want. Generally, one should try to stay with what the posted article was discussing. Suppose you post an essay by Spurgeon, and are discussing the essay with some other freepers. Then, a group of people moves in and begin to talk about the mating habits of the red-necked wallaby. If it is done with the purpose of spamming the thread, then it might be a problem. There is nothing wrong, though, IMO, if the discussion evolves into something off the subject of the article.
One thread right now is discussing the cross..Mormons and total depravity..no one complaining there.