The Chassam Sofer* says that accepting the fact that a king has been appointed by Hashem and has some of Hashem's glory is included in the fact that we must fear and honor a king as a point of fearing and honoring Hashem.
There are indecent people who only fear the king in front of him, like someone who fears a robber, but in secret they mock him. This is not true of decent people, believers the children of believers who know not to question the king or his officers, and one who does ruins their own life.
We see Hashem commanded Moshe to honor Pharoh. And Eliyahu ran before Achav (Zevachim 102a).
And Esther was punished for calling Achashveirosh a dog, Megila 15b.
He goes on to say that when Bava Ben Buta did not to curse a king privately because the bird will carry his voice (Bava Basra 4a), he meant even though the human king does not know what was said, the bird of the sky who is the satan, the heavenly informant, will take the words up to the King of Kings and He will become angry.
*See Drashos Chassam Soffer chelek 3 page 37 column one. See also Shu't Chassam Soffer chelek 6 siman 86 d.h. ועוד אפרש.
See also his drashos chelek 1 page 149 column 4 s.v. איתא where he explains the gemara in Shabbos 33b that Rashbi was hounded by the government after belittling the ruling power, was actually his heavenly punishment for those ungrateful words. He should have learnt from Moshe's dealings with Pharaoh and Eliyahu's dealing with the evil Achav and respected his king. He certainly should not have been ungrateful to the king under whose safety he lived. And, says the Chassam Sofer, even if Rashbi was of the opinion that one may slander a king in private, we find in that sugya Rabi Yehuda arguing with him, and when there is an argument between the two, the ruling is with Rabi Yehuda.
This is all my basic paraphrasing of the Chassam Soffer.
Although he does not specifically address your point, I think it is clear from all this that acceptance of the mortal king under who's dominion you live is a spiritual endeavor and there is a responsibility to protect him.
Even if one would argue that a king who is harmful to the Jews does not get this treatment, which goes against the Moshe-Pharoh and Eliyahu-Achav proofs, remember asset this point Achashveirosh was still good to the Jews. The singular incident of taking Esther, who he did not know was Jewish, would not qualify him as being bad for the Jews. Not that it would matter even if he was.