It is not uncommon in forums to have a pinned post at the top to spell out what is and what isn't allowed to be posted in that particular forum.
I think that would be useful here, if only for people to work out in retrospect why their post has gone.

I've had non controversial posts deleted at other sites, and silly as it is, it is very hurtful. Every post from then on, you wonder if you should bother at all, and you end up leaving.

So I certainly sympathise with you both.