Yes, it is definitely impossible to create a system that confirms a user's selection. It is also impossible to make it so you can resume the subscription if accidentally canceled... or maybe, just maybe there is another reason why they want it the way it is.
Crawl issues I am sure but also user experience issues. Google is sensitive to sending visitors to sites where metrics indicate users do not, like bounce rates etc. I don't use twt but if it is the case you have the be logged in to see anything now, a non-logged in user will click a link from Google hit a login page, and use the back button. I would assume Google will see that as a bad search result and use it less.