I'm not sure what country you are in - but being able to simply report a MAC address to the Police to defend your case is not sufficient.
You have to say who the user actually is. A mac address does not do this. It only uniquely determines a machine.
Failure to be able to identify the end-user means the prosecution will fall back on you. You will have to defend yourself against whatever the user did - as though you committed the crime.
At a minimum, you'll need someone like a phone number. You'll need to look at using something like SMS authentication or asking the user for their actual details (name, phone number, etc).
Or you do what a lot of companies do - give up because it makes the end-user experience yucky, and rely on filtering to prevent them from doing bad things.