I think the original article alludes to this but doesn't say it explicitly:

If they built such a service to let people test their own public keys, the service would actually provide a much bigger service to attackers than it would to users.

Public keys are public, right? There are huge LDAP databases out there just brimming with certificates (i.e. signed public keys) just waiting to be harvested. And most of the people whose certificates are in these databases would not be paying attention to this news, but an attacker certainly would.

You probably see where this is going.