The law in question may have been useful or completely ineffective, but there is one thing which is absolutely certain, and that is that there is no military force on the planet which sends its soldiers into the field armed only with semi-automatic weapons. In the real world, "military assault weapons" are fully automatic weapons, which were already heavily restricted, and which were not affected by this law.
Perhaps Mr. Kerry is hopelessly uninformed, or perhaps he believes that his audience is. Is he an ignoramus, or someone who panders to the fears of the ignorant?