Re: "Internet e-mail is not a secure medium..."
"A Man In The Middle can remove that opportunity."
Sure but that needs active interception equipment in the communications path. If that was done en mass it would be quickly spotted. The purpose of SMTP TLS is primarily to defeat passive monitoring.
That being said, as soon as SMTP STS is fully supported by Exchange I will turn it on and use a proper cert though.
Lets face it, if you are a target of the security services - what ever mail server, OS and firewall you are running, balance of probability is that they can just log right in and get it...