Making it the business's responsibility to identify their customers is an inane idea. It comes from a dying and decaying public sector that is out of ideas and has no solutions to addressing anything in today's environment.

If they're concerned about child porn on Discord, why not just enforce it with audit and sting operations?

In economic theory, if there's some bad outcome you want to reduce, it's usually better to directly target the bad outcome rather than enforce specific behavior. Punish the bad outcome and private actors will adopt the most sensible behaviors to avoid these bad outcomes.