What's the difference? When a stranger who asks you for sparring, how will you know whether his intention is friendly, or unfriendly?
If you hit first "with control", your opponent can feel your speed and not your power. If he is smart and understands that you have no intention to hurt him, the challenge can be ended "friendly" there. If you break your opponent's nose on your 1st punch, the challenge fight may end "unfriendly".
I don't get into street fight that much except when I was young. I do get into a lot of challenge fights. IMO, there is nothing wrong to attack first in any challenge fight.
Wow. Just. Wow.