Earlier quoted context omitted.
For a while gmail had this ui "feature" where or string-of-characters would send an email without prompting. I still fear the web UI. I guess emailing out bullet lists was against the implicit use case the gmail UI team had in mind. Stuff like this definitely changes how tools are used.
This exact problem led to my current behavior that I now use in all email apps: I delete/never fill in the "to" fields leaving that for last. Can't accidentally send an email to nowhere...
Also, when replying to a long mail thread, showing you the previous list of recipients and requiring you to select those that you want to include in your next mail. Could limit CC sprawl quite a bit.