Only justification I could think of is a strict reading of CFAA, where in your exit paperwork the employer commands you not to access any company systems, and the Web site is technically a company system. Though “protected” would be quite arguable there.

I occasionally have crons from my personal infrastructure running into an employer for operational purposes (offsite monitoring or whatever), so I’ve blackholed outgoing traffic to former employers to be on the safe side in case I miss one. So I can see where that sentiment is coming from, though I think it’s a legal stretch.