Even if you accept that it's legal, moral and ethical for the military to secretly remove a democratically elected President, what's to stop any of the conspirators from deciding that Bacco should also be removed from office? Who's to decide if their reasons are valid? Once you've crossed a line it's much easier to do it a second time.
Oh, I didn't say I thought that it was legal or moral for them to force Zife out of office. My point was to specify exactly what crimes Picard and company are guilty of vs. what crimes Section 31 and Ross are guilty of. It's important to remember that Picard and company were not aware of Section 31's plot to assassinate Zife and did not consent to such.
What I would say is this: As readers of the novels, we the audience are omniscient in a way we would not be if we were residents in this fictional universe. As such, we have the advantage of knowing the motivations and goals of the characters who removed Zife from office in a way we could never know someone's true motivations in real life; we know as an audience that the removal of Zife from office was an extraordinary action, undertaken in an attempt to bring about justice to an extraordinary criminal who would have otherwise escaped justice, and that it is not something that those characters would ever do again.
So what I think of these characters and of their behavior is radically different as an audience member vs. what I would think if I were a Federation citizen who does not have access to knowledge of their inner thoughts and goals.
If they were so sure that they were doing the right thing and removing someone from power who has engaged in illegal activities then the co-conspirators all should have resigned as well. By staying in Starfleet they simply proved themselves to be hypocrites. Zife may have broken the law but so did Picard and the rest.
I think that's a completely fair argument to make.
If you could reveal the reasons behind Zife's resignation without risking war with the Klingons, how do you think the population of the Federation would react to Starfleet giving itself a veto over the President?
Again, let's be very specific:
Starfleet did not "give itself a veto over the President." A small conspiracy of Starfleet flag officers, Picard, and the Federation Ambassador to Tezwa forcibly removed him from office, and thereafter never attempted to manipulate or control the subsequent President Pro Tempore or President. "Giving itself a veto" implies the seizure of permanent power over the presidency, and that is not what happened.
And my suspicion is that public opinion in the Federation would be divided. Some Federates would probably approve of Picard and company's actions, believing it more important to bring Zife to some sort of justice for his crimes; other Federates would probably condemn Picard and company's actions, believing that the military should never under any circumstances take any action that threatens the supremacy of the democratic government. And some may react as I do -- seeing a bit of both sides and never quite being sure what side to come down on.
(I wonder what the ultimate fates of three of the conspirators --
-- would impact public opinion. The fact that the current Starfleet C.O., Akaar, was not part of that particular conspiracy, may well affect which side most of the public comes down on.)