WMDs are not even remotely relevant. They are indiscriminate and uncontrollable. But let's be realistic, explosives are controlled as are chemicals, but it would take minimal effort to construct a significant explosive weapon. It happens all over the world in terrorism attacks. Where there is a will there will always be a way. Timothy McVeigh would not have been stopped by regulations, nor would Darrel Brooks have been. All that you can do is change up the method.