The Spartan society thrived in part because they had slaves to do a lot of the hard work for them. While true Spartan males would spend their time being educated and training in combat, slaves would do things like farm for food, serve in houses and even nurse people back to health.
The Spartans treated the Helots (as the slaves were known) really brutally and oppressively to prevent uprisings. One of the things they would do to keep them down was to force them to get debilitatingly drunk and make fools of themselves in public.
This served a dual purpose, as Spartans also used these displays of drunkenness to show young people how an adult Spartan should behave, as self-control was a desired trait in Sparta.
Read more about the ways Helots were mistreated at the source. For example, if that drunk humiliation sounded bad, it’s not even close: Spartans were allowed to kill Helots who were too smart or too fit.