I don't really care about that though. Most people I know have moved on from using email for personal communication and only use it for business. In that situation, I don't really care if my email sounds like me or not. It's just performing a function. It's not a creative expression. It's not any different than Visual Studio completing a line of overly verbose C# for me.
That experience completely differs from mine. Maybe I just prefer email to text or Facebook messages, but the same principle applies to wherever you are writing something to friend or family. Wouldn't you get the same problem, just elsewhere?
Responding to my mother's birthday wishes does seem like it's a different kind of activity than autocompleting C# code, even though both can be executed with autocomplete to get a good valid output.
I am not a good representative for how the average person feels about using it for personal messaging, though. I can see why many people would be against it for that.