I would say that the argument should be for denying public officials the right to conduct any official business, campaigning, and communication with the public

I would say that the argument should be for denying public officials the right to conduct any official business, campaigning, and communication with the public via non-transparent/non-auditable channels such as Twitter. Hypothetically, if Yahoo! automatically bans a suspected spammer account, and it turns out that the account was actually H.Clinton's official address, it shouldn't be Yahoo!'s fault for not knowing the legal identity of the owner -- rather, it should be the owner's responsibility to use the appropriate channels to conduct official communication, and stick to the ToS otherwise.