The original argument is based on the assumption that the opposite of 'revealing 0-days makes us safer' is 'not revealing 0-days makes us less-safe'. I am not sure that is a correct assumption. On the surface it seems reasonable but it is also very simplistic. If one party knows an exploit that others do not, then that party has an advantage over everyone else, and everyone else is less safe from that party. Does that mean less safe in general? That depends on your opinion and relationship with the advantageous party. Those who feel less safe by this are the ones that distrust the FBI.