Strict new European gun-control regulations will take another step on Thursday when a committee of the European Parliament votes on a set of measures. The Parliament and the European Commission already have agreed to the proposal in principle. Prompted by terrorist attacks in Paris and Copenhagen, these regulations would prohibit the civilian use of most semiautomatic firearms. As is typical of such laws, however, they will do nothing to prevent the kind of attacks being used to justify them.

The proposed Firearms Directive...