My MacBook Air has an automatic spelling corrector. I haven't yet looked at how to turn it off, but what I can say is, how incredibly annoying!
At first I thought those typos were my fault. I started worrying about my mental state, watching more carefully as I typed, and realized what was going on. Now I keep wanting to proof-read my texts, just to check one more time that they didn't get modified behind my back - a mild case of paranoia. A minor typo on my part, "fixed" by the automatic corrector, can lead to something unrecognizable. For example, the word "poem", that I accidentally typed as "poen" - a word for which the reader can easily substitute what I originally intended - found itself transformed into "open", and the reader will now be scratching their head (at least it didn't become "porn"!).
How anyone would be willing to suffer such intrusion on our writing, I can't imagine. I will have to poke around to find how to fix this intolerable feature of my new laptop.