Screening doesn't guarantee that a lady will never be assaulted, arrested, robbed, or worse, but it DOES reduce that chance. It's like seatbelts and airbags in a car: there's no guarantee that if you crash you'll walk away uninjured, but your chances are better with them than without. Unfortunately, bad things happen, and it's not even always with new clients. I've read plenty of alerts from ladies whose regular clients went off the deep end.
And if a lady does need to make a police report or post an LE alert, she'll have at least some information to provide -- even if it is just a pseudonym and a hobby email address or cell phone number.
Also, screening helps me avoid finding myself BCD with, say, my dentist.
(Sorry, Dr. R.)