To get the full content and idea one must quote the whole thread started by OP so as to let others know and compare if the thread was being altered from its real content.
You can also archive that.
My question is very obvious, Why can't I delete my own thread?
Maybe there is a problem with this part. One could not delete a thread but the content could be change. If it will be merited and later on the OP change its content like spam post then definitely the one who gave the merit will be reported for not following the protocol on giving merit. LOL. The merit for that post will be irrelevant because its credibility was being altered and this might confused and could be label as merit farming.
IMO, when a post that somebody merited was deleted, it is much more suspicious. I can't imagine if there's someone who would go that far just to spoil somebody reputation, they really have nothing to do in their life, probably :/