If "some wacko" killed his family and himself as a result of your disclosure, would you feel any culpability at all? Of course, you didn't force them to join the site, but you did make the decision to disclose the information.

What if someone joined the site before they were married, but never contacted anyone? Their spouse receives your email, and confronts them. They are unable to convince their spouse that they never cheated, and the marriage comes to an end. Do you feel culpability in this case?