It is not uncommon for people to find that they are more careful when they carry because the act of carrying helps them keep the possible repercussions of their actions in mind.
That said, it's wise to ALWAYS be careful in your interactions with others regardless of whether you are carrying or not. It's unwise to do things that could reasonably
be expected to escalate into a violent encounter whether or not you're armed.
"Reasonably" is the key. Honking at someone who is sitting at a green light is not something, in my opinion, that could reasonably be expected to escalate into a violent encounter. It's clearly possible that it might cause an unbalanced person to go over the edge, but it's not reasonable to live your life assuming that everyone is unbalanced and ready to turn violent at the least provocation.
On a lighter note, your story reminds me of my favorite bumper sticker:
Honk if you've never seen an UZI fired out of a car window!