This is a legislation problem, not a conference problem. I've had my badge scanned for a contest at a European conference early last year and the person at the

This is a legislation problem, not a conference problem. I've had my badge scanned for a contest at a European conference early last year and the person at the booth pointed out that it's pointless because they'll have to delete all that data when the GDPR is implemented anyway. I never heard from them again. Nor should I. The GDPR pretty much got rid of data collection without explicitly informed consent and makes it trivial to withdraw at any point.