With all due respect, I did not. I completely understood--that doesn't mean I agree with the philosophy. As the OP noted, in a smart-minded attempt to keep tire retailers from selling 20-yo tires to people, and as a nod to some of the data gleaned from the Firestone/Ford Explorer rollover mess, the government decided there should be some age limit established for "new" tires.
However, that good-faith approach to address some aging issues, gets turned upside down into you saying that any tire over 7 years old is dangerous. Tell the truth, when someone comes into your shop for an alignment or ball joints or struts, do you look at their tires and if they are over 7 years age, do you advise the customer that their tires are too old and they should buy new ones? That must be quite a moneymaker.
Generally, most vehicles on the road are going to need tires replaced before 7 years because they will wear out therefore it's not really an issue. Regardless, I never said they weren't safe, there is just a greater chance of the tire failing as it gets older. A tire is made of rubber, rubber deteriorates, rubber cracks, rubber is susceptible to UV damage....a tire that is old has a greater chance of failure than a tire that is new. On vehicles which don't get driven often and therefore only get new tires once a decade or so, I will say that yes, the older tires on those vehicles are less safe than a newer tire.