Given that "your current policy" is written by yourselves and that it currently "doesn't allow you to revoke" certificates used to commit fraud or other criminal activities it looks like the only ones preventing YOU to revoke such certificates is that you are willing for the criminals to succeed.
I've seen there's a so called "rationale" explaining why you should help criminals there's another rationale you are not following: "if you don't fight evil you're helping it". Scamming some granma to get their banking credentials is not freedom of speech.