I'm not trying to stir the pot again but it has occurred to me that some of heat in previous postings back and forth might be due to my not having an understanding of the purpose of this forum.
Let me steer the thread in a slightly different direction. The purpose of this forum, at least for the owners, is simply to make money. At the very least, sufficient money to cover the expenses in hardware, electricity, bandwidth, maintenance, and maybe even a tiny (or huge, I have no idea) profit.
If you look around your screen you'll see that the main way of trying to do this is by advertising. While I'm typing this my scrollbar on the right indicates that I'm only viewing approximately one tenth of the total page and there are already three ads moving and flashing to attract my attention. If you're on a reading instead of posting page, the number goes up even higher.
I'm not judging this. Most free forums and other places on the internet use advertising these days to generate an income.
These advertisers normally only pay for their advertising based on page views. The more an advert is seen (and clicked on, hopefully) the more money PPRuNe gets. Do me a favour and hover over one of the adverts on the current page. Don't click on it, but watch where the URL takes you. It's not directly to the company that pays for the advert. Instead, you go to a website of an intermediary first (doubleclick.net seems to be the preferred one right now) who immediately forwards you to the proper website. But through clever usage of links and cookies this intermediary is able to establish that you clicked on an advert showing on a PPRuNe page so PPRuNe is owed money.
Okay, so PPRuNe is helped with as many page views as possible. That means it's in the final interest of PPRuNe to have heated debates here, with lots of people participating and venting their opinion, and even larger numbers of people just reading the discussion without participating. For this reason, PPRuNe should encourage people like David and Sternone (remember him?) to keep stirring the pot, even when it means making an *ss out of themselves.
There is a drawback though. A forum can only tolerate a certain amount of stirring (for lack of a better word) before the regular posters, the ones that really have something to add here, decide to walk away. G-EMMA being a case in point (and I'm glad you're back, G-EMMA) but there are definitely others whose contributions were valued by a lot of people, who decided to leave here.
The Trimming, Landing & Instructors thread stands at just under 5000 views as I write this. I don't know how many views there were before David resurrected the thread on Sep 12, but it will have been far less. In pageviews, it's only topped by the Doncaster Sheffield thread, a bunch of sticky threads (no surprise there) and The Private Flying Photo Album which, as far as I'm concerned, does not need sticky status because it's at the top of the pile almost continuously.
But if you look at the TL&I thread you'll see that near the end it was the same small group posting the same things over and over, with no significant amount of new content or interesting views being added (a few posts excepted). That may well have been in the interest of safety and trying to convince David that he was wrong, but it wasn't in the interest of PPRuNe anymore.
An empty forum, or a forum filled with windbags, means no readers thus no pageviews thus no advertising income. That's where moderation comes in: people like BRL to make sure that the worst offenders, the ones that might turn others away eventually, get banned. First from a single thread, but the next step should be from the forum and eventually from the site. Kudos to BRL for making sure the discussion petered out at TL&I thread. Of course calling the Chucks and Eds of this forum "nazis" did not exactly help Davids case.
So back to the original question. Contentwise the purpose of this forum is not dictated by the PPRuNe management. It's not even dictated by the moderators. It's what we ourselves make of it. As long as you conduct yourself reasonably and responsibly, don't go too far in calling people names, be prepared to accept answers to your questions that may not quite fit with what you know, and are prepared to invest a little time to learn whose opinions can be trusted and whose not, anything goes. As long as it has to do with Private Flying.
And as long as it attracts a large number of readers, thus pageviews thus advertising income.