One important part of the FOID requirement is that those citizen who are legally deemed unfit to possess a weapon or ammunition are denied the FOID card. This makes it easy for a merchant to tell if the customer meets state law to possess a firearm or ammo. What bothers me is when being friends with the local police/sheriff/law authority keeps a wife beater (or some other criminal) from being arrested and therefore losing his FOID card. I have a relative through marriage, who for over thirty years has been in this situation - now and then being beaten by her husband - she's even had to go to the hospital, but the local sheriff closes his eye to what has happened. It is as if the law doesn't exist. Yet if someone would go teach him some manners, he/she would be arrested first thing.
Yes, it is a constitutional right to keep and bear arms, but as of the 21st century, a variety of citizens have forfeited that right; hence, the need to sort out those who are legally entitled to own a weapon/ammo and those who aren't. As for the wife beater, he has no right to firearms/ammo as far as I am concerned. What he needs is a strait jacket - cinched up tight.