Here’s a simple challenge.
Can anyone state clearly and sincerely that their drinking on Purim is only to fulfill the mitzvah, and absolutely not to experience the mind-altering effects of alcohol? If it is not leshem mitzvah, I have no doubt that it is antithetical to avodas Hashem, and is the aveiro that Reb Shmuel Kaminetzky described. Purim is not a heter to let loose with shikrus. It is disgraceful to interpret Chazal that way. Chayav inish l’ivsumai is a positive mitzvah, not a dismantling of the prohibitions against shikrus.