This is really good advice for the workplace and how I would write criticisms for people who I didn't know but wanted the help of. But it is a really terrible suggestion as a norm for Less Wrong.

Here, we've all more or less agreed to not take arguments personally and reward people for admitting they are wrong. Part of what is special about this place is that while it is good to be nice I can focus on whether comments are right instead of whether or not I am threatening a poster's status. As much as possible we try to avoid status maneuvers here - so following your suggestion that we undermine the community's signal to noise ratio in order to make allies (in a way other than being right) is a rather straightforward defection.

This doesn't make being mean is acceptable. I agree with Alicorn's classic post. But you seem to be advocating not just taking steps to avoid being mean but to expend extra efforts and page space on meaningless niceties instead of making forthright and respectful comments. While perhaps too confrontational in most workplaces nearly all of the examples are just fine here. If you're going to bother correcting spelling at all (and only in certain cases is it worth it) be brief for goodness sake!

I hereby pre-commit to downvoting anyone who corrects one of my many spelling errors by writing a paragraph like

Hey Jack, I wanted to give you a heads up. I saw your recent post, but you spelled "wisen" as "wizen" - easy spelling error to make, since they're uncommonly used words, but I thought you should know. "Wizen" means for things to dry up and lose water. Cheers and best wishes."

...

Wisen, not wizen.

will suffice. If you can't leave it like that "Wisen, not wizen, you idiot." does less psychic damage than making me read that paragraph. The funny joke that was made in the original example would be the best, though.