Fact of the matter is, at the time, all posts that were replied to in the last 40 or so hours were deleted, regardless of topic. Frankly, for such a thing, it's far more likely to be operator error as opposed to some sort of cleaning policy, as some controversial topic were left while harmless ones were deleted.
It was probably honest mistake, it's just annoying that they refuse to own up to it.
That said, the thread you made is actually somewhat controversial, not in term of topic but in term of possible reactions, I'm not going to go in there because I don't want to start an argument over that. It's also amazing how you tunnel vision on the one thread as opposed to grasp the problem at large, which mislead people who read your complaints as to what actually happened. People will tell you that YOUR thread have problems (aforementioned controversial nature) while not realizing what have actually happened--the mass deletion of threads regardless of content and topic.
And from there, some of the mods who don't actually know what have happened would get the wrong impression as well and therefore think you are complaining about stuff that's irrelevant and/or shouldn't be complained about, and proceed to lock your thread (along with that other thread regarding stuff being deleted in general, that was also tunnel visioning on jut two threads, which unfortunately were both potentially controversial). This mean that they would not be performing any sort of internal investigation as to what have actually happened and, for the most part, honestly believe it was just regular moderating. And the person who made the operator error will get away with it because none of the mods/admins etc realize that is what have happened. And a few week down the line, it will probably be impossible to investigate.
So guess what, you are HELPING them bury their mistake. Congrats on your efforts, they should give you a reward for it.