You are not citing Red Flag Rules. You are citing firearm purchase rules. Red Flag protects personal identifying documents and when they may be required and how they must be handled. A SS card or even number is not a requirement for the transaction as prescribed by federal law and is therefore improper to collect.The rules are for the minimum requirement for ID. Not the maximum. I can require only Real ID’s or regular driver’s licenses with passports in leu of the Real ID in my gun shop. That isn’t illegal. But if all I did was require an old high school ID I would be in violation of federal law.
I don’t know why this is even argued. The bottom line is that you can boycott them because you don’t like their policies. I boycott a local gun shop / range by me because they are overpriced and enforce ridiculous gun rules at their range.