Earlier quoted context omitted.
I don't think slippery-slope is an appropriate argument to make here, or really anywhere. To answer the UI elements on the bottom, I'm not sure I actually press the Send button at all, instead opting for a keystroke depending on the client. The physical analogue I base my request off is the order I fill out a letter or card--I write my message, then I sign it, and then I seal and address the envelope. Beside that, wh…
First of all, i bet you that much more users click on a send button then press some arbitrary key combination. Second i bet you that most people find the send button easier when it's somewhere they expect. Where the other buttons are. Third, physical analog bla bla, really... Nobody thinks "hey i am writing an e-mail, that's just like real mail, EXCEPT i write on a keyboard, look on a screen and everything else i tou…
I'm sure I'm not the only person who has change (or left blank to begin with) the subject once I've written the email.
Also I've observed a lot of people who write the content first then fill out the top (To, CC, BCC) after. Often the content effects who should/can see the email.
The current UX is wrong given mis-sending, mis-addressing still occurs.