One strategy for explaining the problem to non-technical people is by comparing regular email to the walled-garden email used by some banks, phone companies, and the like--where you have to log into their website to see your 'inbox' and use a web form to send messages. It's super annoying and the other party has complete control of the communication channel.
"Dynamic email" could be implemented to inject this kludge into your email client, giving the AMP sender (who likely has more power than the user) the same level of control over the channel. Imagine opening your email client and finding a message which asks for two security questions and a captcha, then lands you in a messaging interface which limits you to 200 characters and denies basic affordances of email like archiving and forwarding.
I find the arguments that email is already mutable because images are externally-loaded unpersuasive. In 2013 Google started caching images in gmail "to protect you from unknown senders who might try to use images to compromise the security of your computer." [1] Email marketers were upset at losing engagement metrics. Now a practice that used to be considered abuse is being rolled out as a feature.
[1] https://gmail.googleblog.com/2013/12/images-now-showing.html