They didn't have to ban DS altogether. If they made the case that Interceptor was good enough that they don't reasonably need to have level 5 ballistic protection, then I wouldn't disagree with that.
The F-22 is the world's best fighter, but that doesn't mean that I would support it over the F-15 and F-16. It does make sense not to build many F-22's because five F-15's can do much more than one ultimate fighter. Because the F-15 still is 92/0 in combat, you don't really need a fighter that can outperform it for four times the cost.
Same thing could be argued with DS.