Have you actually read the CAN-SPAM Act? Do you know that it doesn't restrict existing business relations from sending you mail? How did you get on the ACM TechNews list if you didn't sign up for the list or sign up as an ACM member?
It's really about whether the email is commercial or relationship content. This is a subjective point for mixed emails, and the ACM TechNews email does in fact mix the two by containing banner ads and links to the ACM's social media sites. If you are sending "relationship" email, you are exempt from some of the act's restrictions. It does seem that if you are classifying it as a relationship email then you only need to obey the truthful routing information. However, being unable to unsubscribe I believe is also a violation regardless of the status of the email, but I'm less clear on this.
I went halfway through signing up for an ACM account once. I believe I never agreed to the final conditions or anything. They send me e-mails every once in a while about how they "noticed" I didn't finish signing up.
This reflects very poorly on the ACM and has been a constant point of frustration for me. After letting my membership expire I've made numerous attempts to unsubscribe to their mailing lists and have had no success.