IMO the 3' rules that states are passing is simply a sop to folks that want them, and so politicians can say they did something for their bicycling constituents. They might be defended as educational in terms of establishing a safe standard (which IMO they don't), but since there's almost no effort to publicize them. How is any driver supposed to obey a law that he has no idea exists?

In most (all?) states the standard rules of the road, give right of way to the car vehicle being passed, and make it the responsibility of the passing car to do so safely, and appropriately for conditions. So no new law is actually needed.

Enforcement of a 3' rule is almost impossible except in those rare conditions where a cop happens to be there and has a good line of sight. Of course, there's the possibility of a ticket when there's contact, but we don' need a new law for that.

If it were practical, maybe having every driver ride a bicycle 1 mile on a fairly busy road once a year might make a difference. Likewise some cyclists need to understand what the traffic mix is like behind a wheel.