I didn’t say drinking alcohol was a sin. I said getting DRUNK was.
Anyone who believes in getting intoxicated (toxic being the root there) for religion is an idiot. period.
Do we learn not to do anything else by doing it? murder? rape?
of course not
As they say, take it up with the big guy. As for Jews, it isn't a matter of belief as much as it is a commandment which is part and parcel to the celebration of Purim. There are 4 glasses of wine involved in Passover celebrations and it is the height of error to become intoxicated or even impaired as this would be an affront to the observance and the sacred moment. The Passover celebration is the substance of the Christian last supper and the foundation of the practice of communion, except if anyone has ever attended a Jewish Shabbat service they will note that Kiddish and Motze are always part of this service (Bread and Wine and the blessings said over these) and this practice is thousands of years older than Christians have been doing it in the form of Communion.
As far as your point about what does one learn by drinking to the point where one cannot tell Mordechai from Haman, this is a qood question. First, as it is a commandment, in that we follow it we keep the commandments and remember what we are asked to remember. So, remembering the 10 Commandments is but part of remembering all of what we learn to live a holy life. We learn that people who are drunk do silly things and we learn that the next morning it is time to suffer the hangover. Most importantly, we learn not to look down our noses at others who suffer and make terrible mistakes, and we learn that this is only acceptable behavior one night a year. The rest of the year, keeping the commandments means keeping our heads about us. Thats enough for me, but if you are really interested, I am sure I could find commentary on the why of this because it is not something that is a "mysterious" commandment, ie one that is bizarre but done regardless of being insane. It is odd though, and much time has been spent by a number of scholars explaining this requirement. You will find in time and in various faiths, this same festival is recreated in this same time frame under the heading of "Carnival" in preparation for the Lenten fasting that precedes Easter, which by the by, is in lock step with the Passover observance which prohibits leavened bread in any form.