Quite a few different angles here...

First, I'm sure you wouldn't bother with an Anonymous or 5-minute Initiate question that's obviously thrown out with little regard for punctuation, spelling, or grammar. Obviously they don't care, and it's best that you allow them to present their sloppy selves honestly.

For correcting typos vs. spelling errors, vs. wrong word choice, I suppose there's an increasing chance of offense (not correcting the UKers, I know it's 'offence' over there). On the other hand, I don't get it. Why would having an error pointed out to you be offensive? Personally, I might feel slightly embarrassed, but I'd rather get it corrected sooner rather than later. You can be sure for every one who corrects you, there are dozens of others that may consider you ignorant or stupid. Is it preferable to some people to wallow in their own ignorance rather than deal with a momentary pang of embarrassment?

That said, I almost never correct others' spelling, typos, or grammar. If the writer wants those things right, they can do their own checking.

p.s. I really don't like using 'they' instead of 'he' or 'she', but the present alternatives are worse.