No, there is a third issue:
Issue 3: the mumsnetter on duty giving in to a particularly, erm, insistent op.
So if I email and ask politely for my thread to be deleted (either because I am upset, or have made an arse of myself), I will politely accept a polite refusal. As Freddie did with hers. See, all PARD-like 
But if I spit out my dummy, have a hissy-fit, start insulting everyone and everything onthread, start naming names, repeatedly email mumsnet, and pretend that someone I know has seen the thread, then it is easier for the mnetter on duty just to say "fuck this for a game of cowboys, I'll delete the fecking thing".
Which I sympathise with.
But in that case, you should say "We don't normally delete entire threads, but if you are precious care enough to go completely bonkers, we will probably give in to the pressure.