‘course—People could just choose to opt out of Facebook and go elsewhere.
“Sheryl Sandberg: Facebook users would have to pay to opt out of ads”
You cannot delete your Facebook account. Their version of delete is you can permanently suspend your account.
What FB should do is let anyone who has joined from day 1 until today, opt out and delete, then put the new rule in starting tomorrow. That would be the fair way to do it.