I do edit questions for grammar for two main reasons¹. First, I really hope it will help the OP. Second, I think grammatically correct language represents a higher standard, and I know quality is an important issue for the powers that be at Stack Exchange.
Why do some users reject editing?
Lately, though, I've noticed when I've edited posts that have had blatant and/or extensive grammar errors, the LULZ, or have been in need of ESL assistance, the OP is rolling my corrections back to their original version, incorrect SPaG² and all. What's frustrating is the OP then leaves the post in its original sloppy state and makes no attempt at corrections himself/herself. On a few occasions I've had my edits rolled back, and then will notice another user also attempted to edit the same post, but the post is still in its original incorrect state, meaning the OP rejected suggested edits at least twice. So the OP is actively resisting community assistance.
I have no problem with an OP rolling back my edits, only to make their own corrections. That's awesome and I think it's great to see an OP take responsibility for making their own corrections.
So, is there anything we can do to encourage all members of this community to remember that we do have a Wiki-like set up here and to help users to be more amenable to grammatical corrections, to not rollback edits that are meant to be helpful?
First, I do want to say that whenever I edit a post, I always try and work within the original spirit of the OP's post. When I edit for SPaG, I try to be extremely thorough, so multiple edits on the same post won't be necessary. However ... is this considered okay? When does it cross the line into over-editing? I will correct SPaG, and if I see a word being used incorrectly, I will fix the word, too. For example:
"I did not give you my constant to edit my George R.R. Martin answer to add a picture of Harry Potter" becomes "I did not give you my consent to edit my George R.R. Martin answer to add a picture of Harry Potter".
Another type of change I will make is to clarify speakers and characters in sentences if I am positive I know which character is doing or saying what. For example:
"First, he cast a fire curse at him; in return he hexed him and gave him a magnificent rack of antlers. His curse also hit the Fountain of Magical Brethren, but he repaired it" becomes "First, Voldemort cast a fire curse at Dumbledore; in return, Dumbledore hexed Voldemort and gave him a magnificent rack of antlers. Voldemort's curse also hit the Fountain of Magical Brethren, but Dumbledore repaired it".
Is this kind of edit inappropriate or too extensive? Where do you draw the line with editing?
¹I know I'm not the universe's gift to grammar :P
²SPaG is Spelling, Punctuation, and Grammar. I use this code for the "reason for edit" box and have had a few people ask me what SPaG means. So I thought I'd just mention it as an FYI.