ח וַיֹּאמֶר הָמָן לַמֶּלֶךְ אֲחַשְׁוֵרוֹשׁ יֶשְׁנוֹ עַם–אֶחָד מְפֻזָּר וּמְפֹרָד בֵּין הָעַמִּים בְּכֹל מְדִינוֹת מַלְכוּתֶךָ וְדָתֵיהֶם שֹׁנוֹת מִכָּל–עָם וְאֶת–דָּתֵי הַמֶּלֶךְ אֵינָם עֹשִׂים וְלַמֶּלֶךְ אֵין–שׁוֶֹה לְהַנִּיחָם
8. And Haman said to the King Achashverosh, “There is one nation scattered and dispersed amongst the nations in all of the states of your kingdom. And their laws are different from all of the nation, and the laws of the king they do not do, and to the king there will be no loss in keeping them.
According to Rabbi Dovid Feinstein, Haman consulted with the king because he wanted to convince him that it was not barbaric to kill out the Yehudim in an act of genocide. After all, Achashverosh, like most leaders, was concerned about how he would be remembered in history.