I am Not Happy about this. Deleting posts is a couple of rungs up the ladder from deleting comments. And how we feel about that is spelled out in the user info. I'll add the deleting posts thing later today to make it more clear.
I don't know the motivations behind the deleting (and maybe it was just a mistake, which is fine cuz we all make 'em) but if it had something to do with the conversation not going the way you wanted it to... well, you're just going to have to suck that kind of thing up. This isn't your personal journal, it's a community. And one of the things this community is founded on is mutual respect and open discourse. Discourse cannot be open when the discussion dissapears.
There are not many things that will get you banned from this community (because I hate banning, it goes against our vision) but this is one of them. And for this, there is only one warning. Consider yourself warned.