In a situation like that the OP just needs to learn to articulate their argument better. A clearly worded, concise argument is very difficult, if not impossible for someone else to misconstrue.
Specifically on topic, in general it all comes down to who actually has ownership of a thread (this is in a general sense because we all know that SE "owns" all the threads on this forum). Does a thread belong solely to the person who started it, or does it belong to the community of people that are taking part in the discussion? I believe that it belongs to the group because often a thread can move on to cover subjects not strictly related to the original post, and still be extremely valuable and useful to the community as a whole. As a result giving the power to lock threads to a biased individual, and the OP is always a biased individual, is inherently a bad idea.
There is a reason why there is a neutral group of moderators appointed to, well, moderate the forums. Ideally they are able to look at every thread and post from an unbiased perspective and make judgements on what needs to be moderated or left alone. I've never seen a successful form that gives this kind of authority to all the posters. I'm not saying that kind of forum can't exist, but it requires that the overwhelming majority of the posters actually behave like adults, and unfortunately that just won't happen here.