On one on line community I not only had to register but reviel to the one professional running the site what my actual real life address was because they sent an acceptance letter by snail mail and instructions for confirming my membership by logging in with a password contained in the snail mail letter.

That in itself prevented some (not all) people from coming on to start trouble because the one professional had who the person really was and confirmation since the person had to log in the first time with the given password.

Email addresses can be faked.

I have an email address posted. That is not my personal email. it is one I use for my writing, and various groups so that people have a way to contact me about groups, my writing and so on without it interfering with my personal life. I recieved that email by opening an email account using the pen name that I use for writing. Email services do not ask for ID varification.

a person can get a po box but they have to show the postal worker thir ID and so on to get those boxes so when a website administrator sends snail mail they are 98% guaranteed the person is who they say they are.

The bottom line is that even with snail mail registration protocals and email addresses when on line it is best to use the common sense rule of non disclosure. That way on line members are protecting themselves and will not have a problem in their real life such as what happened here.