I still vehemently disagree (and am sad that such uncharitable motives are ascribed to me when I have explained why I'd correct typos and it's got nothing at all to do with wanting to "educate them"), but I can see we shall just have to agree to disagree. 
Do you really not see how something like the above, regardless of intention, comes off as condescending? This isn't about intent. This is about perception.
If I correct a typo, I don't point it out. I'd just quietly correct it like above. Because I agree, what you did
would be rude and condescending (note, not calling you either, I knew you were just making an example), and most definitely not be a "polite fiction" that the typo never happened in the first place.
I Still vehemently disagree (and am sad that such uncharitable motives are ascribed to me when I have explained why I'd correct typos and it's got nothing at all to do with wanting to "educate them"), but I can see we shall just have to agree to disagree 
You may still disagree, but would you continue to correct posts knowing that so many people believe that it's rude?
Not on purpose. I may forget as it's become such an ingrained habit of mine. But if I remember (and I promise I'll try!) I'll just refrain from using the quote feature. Since I, personally, think it's unkind
of me to notice a typo and embarrass the poster by repeating it, I think that's the best compromise

(Emphasising that it's a personal quirk, and I don't think it's unkind of anybody else to notice a typo and not correct it... although I hope they would do me the kindness and correct mine, since I'll try to do them the kindness and not correct theirs. I don't actually expect that to happen though, as it would be impossible to remember who wants what.)