We have a generally accepted and established norm on editing the content of questions, as addressed in this answer to the question http://meta.math.stackexchange.com/questions/4255/ and in this answer to the question http://meta.math.stackexchange.com/questions/3163/
But I recently saw something, and I wonder what community feels. So I think of this like a case-study.
In the question - How did it happen that base 10 went on to be the most popular? (which happens to be closed now) - one user happened to write two short answers to the question. Another user edited the two answers: he erased one and edited it so that it read "Answer blanked in preparation for deletion", and added that content to the end of the other answer. He then flagged that answer for deletion. This had the interesting side-effect of causing other people to flag it for deletion as well (as it no longer had any content).
I brought this up in chat, and another user rolled back the two answers. I then posted a comment. As the question is closed as a duplicate, it won't be attracting much more attention, so this is all a bit under the rug.
In the question - Is trying to prove a theorem without Axiom of Choice useless? - one user happened to write two short answers to the question (Both answers happen to be deleted, so only 10k users will be able to see them, but this is the only example I remember exactly). In this case, first another user left a comment, and then I left a comment suggesting that the user combine the two answers, as I thought them very similar.
The answerer decided that he did not want to combine his two answers. Both answers got down-voted. As it happened, both answers were later deleted by a moderator. (There are some circumstances surrounding this case that some may know, but that I do not think are relevant to this discussion; what I'm trying to get at is that there was a request that the two answers be combined, and then they weren't, prompting the follow-up question "Now what?")
While it is conceivable that a slightly more experienced user might simply rollback their two answers if they thought that someone treated their answers unfairly (as might happen in Case I), this wouldn't be possible if a moderator deleted the answer. And this is more likely because the edited answer would attract flags about its deletion.
On the other hand, if comments were made suggesting that a user combine or delete answers, and then ignored, it's unclear what would then happen. I do not think that a single shoe will fit, and should be handled case-by-case.
I feel that for a user to combine two answers of another user is over-editing with respect to the line separating editing for readability and editing content. Put another way, I don't think that we should alter posts in this way without the OP's consent.
Is this what the community thinks?