I am usually opting-out of body scanners (in the EU its still optional). But at some airports the security people seem to not know that it's optional. By now I

I am usually opting-out of body scanners (in the EU its still optional). But at some airports the security people seem to not know that it's optional. By now I always carry a letter from the federal police (responsible for border + airport security) explaining that it's optional. At Berlins airports they usually ask for a reason why I opt-out of body scanners, which is ridiculous, as one needs no reason to NOT do something that's legally optional to do.