It's understandable for the affected individual not to behave logically, and for the society to find release valves. That's different from the society choosing the particular release valve of battle to the death.
You can try to outthink it all you want, but that's how it works for them, as seen in the episode. They all go through it, and as a society, they are anything but rational about it. I'll reiterate, this sort of thing may even have a religious significance to them.
Bottom line, it's all about the contrast. They bottle up their emotions most of the time, but when the combination of biology and time-honored ritual causes them to let their hair down, look out!