Testosterone and insecurity.
Some people enjoy fighting "arguing" socially, but most are just insecure about who they are.
Speaking your mind with an insecure person can get you a verbal attack without ever wanting a confrontation. That's why its best to keep opinions to a minimum in public circles.
Youth is another reason for picking fights. Young men often want to prove their ability to stand their ground against others. Think of kittens learning to pounce. They are practicing. Topic makes little difference.
Just walk away or ignore the attack and its often gone quickly. Put up with it, even without responding, and you are inviting them to do this with you whenever they choose.