1) Confidence - biggest reason really. The process of breaking down your ego and building it back up is priceless. I've always told people that practicing Judo (and wrestling) is like giving yourself a gift, that you use every minute of every day. Once you have it, you never lose it.
2) Situational awareness - You build this over time and it helps. There are countless fights and other dangerous situations I've been able to avoid just because I was more aware and confident that I wouldn't get smashed by some drunk.
3) Cross the border. - Sometimes we take it for granted how safe it is in USA/Canada/Western Europe. Your mind might change pretty quickly on a dark street in Mumbai
It's not all for fun & fitness. You use your experience more often than you think.
"i always question why grown men ask about self-defense. unless you work as a cop or in the protection/military fields then it is really odd to me that grown men want to learn to beat somebody up."
Self-defense has nothing to do with learning to beat somebody up.
Wow, people are really attacking the original poster. Even though I don't think about "fighting" or "self-defence" when training, it's a motivation. Martial arts are fun, are great for making friends and getting in shape, but in the end it's about fighting. Who wants to waste their time with an art that isn't practical?
Yes, judo is good for SD. A good stand-up grappling game is important, and a throw can hurt someone on the streets.
A grown man may well benefit from self defense knowledge especially depending on where he lives. And judo teaches many good habits relating to sd ie confidence, awareness, tenaciousness. But good sd teaches the mental toughness and smarts that's more important than just tactics.
The thing with self defense courses is that you will probably forget what you've learned when you'll need it.
Randori,newaza, you learn how to defend against chokes it
becomes a natural reflex over the years. You don't learn self defense in a class it takes time to build in.