I think it was pretty fucking obvious from his reaction during the game as to why he did what he did. Pedersen had a horrible little smirk on his face too and like Arteta I consider myself a mild mannered person, but if someone did that kind of shit to me on the footy field, then they would feel the wrath too.
And yes, I'm trying to defend him. Can you imagine what we/he would be like if that tackle had put him on crutches.
As for a Red Card - Yep, he should have got that too (Arteta that is) and possible Pedersen.