Why do you get in more trouble for retaliating when someone clearly did something wrong in first place?

Well, there's a little something called, "Assault and Battery" that you can be legally charged with.  Besides, there's no law against cheating on others or stealing your girlfriend, even if its morally wrong.  If she really loves you, she'll shrug off their advances.  If not, she wasn't in love with you in the first place.  

Also, if someone steals your cash, you can take legal action against them. However, beating them up will just get you in trouble and give them a chance to act smug and play the victim.  

Largely because in your first example, flirting is not illegal in any way, and assault is. They did not in any way initiate a fight. You did.

If you could prove you were scammed, you could report to police. Again, assault is illegal.

When someone is flirting with "your" girl it's up to her to explain that she's not available. If she doesn't do that then your problem is with her, not the guy who's flirting. Likewise white collar crime doesn't rise to the level where any civilized person would think violence would resolve it. It's because societies have determined that those who try to use violence to solve problems are mentally unhinged and represent a danger to the rest of us.

The "initiator" is the person who started the PHYSICAL "fight."  The other person could be an instigator, but that person is NOT the "initiator."  I have no idea what the people who support the "initiator" have to say.  The probably wonder why you react so violently. They probably, like me, assume you are very, very insecure in your relationship.

The law is force against like force.  If you are so insecure that someone flirting with your gf in a bar causes you to react with physical violence, you have issues.

Same with people involved in scamming you.  You file charges.  You attempt to be smarter the next time around.

Your, you're.