I don't think it's atrophying. We said the same thing about spell checkers, and my spelling seemingly hasn't suffered.

I'm not a native speaker. It's nice to have training wheels sometimes, even for a language I'm familiar with.

These tools will only become more pervasive, so why does it matter if that part of the brain "atrophies"? I'm sure people had the same worries about mental math during the rise of the calculator

Just imagine how flaccid the math part of most of our brains must be. Quick! What's 67 * 42?