An incorrectly autocorrected word is far worse in terms of negative user experience than a misspelled word not autocorrected. I say underline the word in red and leave it to the user to tap the underlined words to trigger autocorrect.

I don't think that it what he is saying. I agree with him and the point is that a misspelled word is not going to inhibit the communication between two friends. Changing a joke/inside/slang word to something the phone thinks is "correct" does inhibit communication. They are arguing that auto correct is worse in this context. (Although, it makes more sense in an email or document editing setting)

This is ignoring the fact that autocorrect can fix massively incorrect words. If you’re off by half a centimeter for a while word it could be complete gibberish if not for autocorrect.