Maybe software can be tweaked to give an option to the thread starter to categorize his thread as "news", "info", or "discussion". I had seen such facility in a certain forum. Such categorisation helps later when someone else wants to retrieve the information through search.
Some people like to visit the forum to stay in touch with the latest updates on a certain topic which these "zombie" news or info threads provide. Some others may be interested in only debates. To each one, his own. Any thread classified as 'discussion', can be closed if it remains inactive for a certain period(may be 2/3 months), whereas 'news' and 'info' threads can be allowed to die on their own.
About religious discussions:
Purely religious discussions, do not harm anyone and are frankly implicitly tolerated in our forum. For example, if I start a new thread about the sufism and its glory, there is a greater chance of it being tolerated and allowed.
But those topics where religion influences the society are not tolerated and disallowed. Religion and its influence on politics, language, behaviour, beliefs, economics, culture, .....etc are implicitly and explicitly not tolerated. For example, if I were to a start a thread about political islam, there are greater chances of it being closed.
This is an interesting phenomenon!! Because, from an absolute point, a secular atheist forum(the forum as an organisation is secular and atheist because it allows people or ideas from all religions but does not adhere to or sponsor any particular religion or god) should be discussing only those social, political, cultural, linguistic....etc topics where religion has influence and should be avoiding any purely spiritual topics. To the contrary, we see that a religion's spiritual side is allowed and its other parts which have a direct bearing on our society's functioning are ignored, even though they are the elephant in the room.
Now to the topic, here is my humble suggestion to increase debates: I think the forum is over-moderated. Thread deletion and post deletion seem to happen far too frequently on the forum. Every post is expected to be of the high quality with some purpose. Every poster is expected to be lucid, knowledgable and polite. I sure, the mods have the right intentions, but what it leads to is an uncreative, boring, symmetric discussions which lead to neither solutions, nor excitements. Thus, I feel the mods need to chill down a bit!! Its just a forum, people have to exchange ideas for the forum to serve its purpose, otherwise its futile. The rules need to be minimal. Mods need to be invisible.
Lastly, mods should not be allowed to participate in discussion on a certain thread and simultaneously moderate the thread. Its a clear conflict of interest. Its like an attorney is allowed to be the jury. For the poster who debates in this kind of situation, its like arguing with god.
PS: Agree with suggestion that stats like top poster should go.