So who cares if you write your email in text mode but browse the web with Chrome/Firefox? No offense against Mutt... I can understand that some terminal pros like it but I cannot understand using it for security sake. So what happens if you want to view a html email? What about mail on a mobile phone (I guess security experts do not use them)?
And mutt has other attack surface because it is using the terminal. Look here for a Ubuntu security notice about mutt: http://www.ubuntu.com/usn/usn-2440-1/ Now I smile because gmail is not affected by that!
This is all not practical for 99,9% of normal users out there.
If you care about security do not let the paranoia control you. We need to improve security for the normal users out there. Just my opinion.