The people misusing the air guns were children, who according to the law should not have access to them anyway. Therefore, instead of banning them the government should be trying to enforce the existing law.
The British government has always disliked people owning firearms and they have used the massacres to clamp down on them. It is not a liberal policy, it is an authoritarian policy. But since the people who committed the massacres owned their firearms legally then prohibition makes more sense than it does for air guns.
The widespread availability of firearms would be bound to increase the murder rate, so I still support firearm controls. Because there is no tradition of buying firearms for defence then I doubt that liberal gun laws would have many positive effects, apart from making it easy for criminals to arm themselves.