It's not hexus forums policy (please note, hexus owns the forums, but the forums and hexus are somewhat distinct), but it's something that most moderators would bring up if a thread started to get derailed and people complained about the direction of thread - remembering that all moderators and admins act on their own judgement, although informed by the direction and general ethos that the forum owner expects us to maintain.
In this case there's two arguments to be made. The first is that a thread title is likely to direct the content of the thread, as people will often enter a thread and respond to or debate the thread title - and inasmuch as that happens the title of a thread will often inform the content of it. The second is that common decency suggests that you should at least read the opening post of a thread before commenting on it, as the title is necessarily short and a thread starter is likely to have expanded on their point.
So, if the OP is actually a more complex consideration than can be expressed in the title of the thread, but people come in and simply try to debate the thread title while ignoring the OP, that's slipping below the standards of common decency, which is the minimum we'd expect at hexus.
In this case, it was pointed out very early in this thread that there are several other threads already open that discussed the topic more generally, and the OP clearly asked a question directly related to the article linked. So whilst I understand the temptation for people to bring the general debate about EU democracy into this thread, I don't think this was the correct place for that discussion to be picked up, and I can understand the OP's frustration at this thread essentially turning into just another debate about the rights and wrongs of EU membership (if slightly more focussed than the others).
All that said, I don't think anyone's covered themselves in glory in this thread. Unsurprising, given the emotive nature of both the subject matter and the wall-to-wall media coverage of it, but unfortunate, nonetheless.