Anonymous/pseudonymous speech is a long standing tradition of free speech, which many of us are enjoying right now right here. However, there is a difference between private conduct and conduct as a government agent. Government is an agency owned (ultimately) by the people and created by them to achieve certain purposes. To further those purposes, people can institute rules of conducts for the agents of the government. Not using anonymous/pseudonymous speech while performing government duties may very well be one of these rules. Not because government is always evil, but because we think our goals will be achieved better if government would act openly and identifiably and the reasons why we value anonymous/pseudonymous speech largely do not apply to the government actions. The government as such does not have inherent rights that people have (though its agents have them as people, but when working for hire as agents they may be bound by stricter rules than in their private life). That is the difference.
