"If you believe that any of the current replica BB guns are anything beyond playthings you're sadly deluded …"

The law may be an ass, but the law defines airguns as firearms, not playthings.

As an example of how your logic could be applied, what about clay pigeon shooting? it's an activity where people use a firearm to shoot at targets.

If using a co2 replica is also an activity where people use a firearm to shoot at targets, surely your definition must make shotguns mere playthings...