Musar על סוטה 82:10

A man should undergo danger rather than be guilty of this sin. And our Sages, of blessed memory, said, concerning Agrippas, that when he was reading the Torah and came to the verse, "Thou mayest not put a foreigner over thee, who is not thy brother" (Deut. 17:15), his eyes shed tears. Those who were near him said, "Do not fear Agrippas. You are our brother." In that hour the "enemies of Israel" [a euphemism for the "Chidren of Israel" where anything dire is said concerning them] became liable to destruction for they flattered Agrippas (Sotah 41a-b).

The ninth category of flattery is he who honors the wicked because he wants to preserve peace. It is true that he does not speak good of the wicked and he does not conduct himself in any way that would cause people to think that the wicked person is honored in his eyes, for he does not show him any honor except in the way that people honor the rich, because their path has been prosperous, and not because of their own merit. Yet even in this there is sin and guilt, for it has never been permitted to honor the wicked, except for terror, that is to say, if one is afraid that the wicked man will injure him or cause him a loss at a time when the hand of the wicked is mighty. Therefore it was permitted to honor the wicked man as people respect all men who are mighty, but he should not praise him and should not speak good of him to people. And so said our Sages, of blessed memory, "It is permissable to flatter the wicked in this world" (Sotah 41b). But there are wicked whom we may not flatter. Whence do we derive this? From Mordecai, who was advised to flatter Haman, to which he retorted, "Thou shalt not seek their peace nor their prosperity" (Deut. 23:7). And they would say to him "Our Rabbis taught that we must flatter them for the sake of peace," but even then, Mordecai did not want to flatter such a wicked man as this.

Rabbi Simon, the son of Halafta said, "From the date that the power of flattery grew strong, laws have been twisted and deeds have been perverted, and no man was able to say honestly to his companion, 'My deeds are greater than your deeds.' " Said Rabbi Elazar, "Every man that has flattery in his nature, brings wrath upon the world," as it is said, "But they that are godless in heart lay up anger" (Job 36:13). Not only this, but his prayer is not heard, as it is said, "They cry not for help when He bindeth them" (ibid). And even the unborn children, still in the wombs of their mothers, curse him, and he falls into Gehennah. And everyone who flatters a wicked man falls into his hand. And if he does not fall into his hand, then he falls into the hand of the son of the wicked man, and if he does not fall into the hand of his son, then he falls in the hand of his grandson (Sotah 41b). Every congregation that has within it the trait of flattery is as loathsome as a woman in her impurity, and in the end will be exiled (Sotah 42a).