this is not 'taking any step other than sending a reply email' and it's the standard way mailing lists managed with mailman or majordomo or ezmlm have worked for quite a bit longer than 20 years

also, according to that page, the can-spam act only applies to 'any electronic mail message the primary purpose of which is the commercial advertisement or promotion of a commercial product or service', not to mailing lists

something can simultaneously be standard practice in one community, essential for security, unusual in another community, and illegal in many parts of the world, though nobody seems to have found any laws against the standard mailman unsubscription mechanism in this thread

it is understandable that people who are not familiar with a cultural practice might seek to marginalize it, but that does not make it right

i don't really care about making life easier for people who send email advertisements (a cultural practice i am sadly all too familiar with) but i think discussion email lists are important and valuable, even if you personally don't participate in them

hopefully people like you won't be able to figure out how to subscribe to the mailing list in the first place