isnt robin supposed to be a friend, too!? Also they were together so she should feel protective of him!
but we might see more in the upcoming episodes...

His feelings are understandable, but he was unfair in not treating them as equally culpable.

I think he was harsh on Barney, but he pretty much did nothing to Robin... that bothered me.

Why is he was too harsh on Barney winning? I swear, I am going to hunt down everybody's ex boyfriend/girlfriend and sleep with them just so they know how much it hurts! ................. Ok maybe I won't do that. That would make me a bit ......... prostitutey. Anyway, he was too lenient on Robin however I think that's because he knows it's not something Robin would normally do.

NO,NO,NO,NO,NO
Barney totally deserved everything!!!
I mean it wouldn't be fair if they would go out with Robin, be a real couple or something, but just one night? with his best friends ex gf?

I agree with Saul_Mikoliunas. I think he was too lenient on Robin, they were all a group, by that moment Robin was as much of a friend as Barney was, although I understand that it hurt more coming from Barney.