The argument for a yellow in that situation is that regardless of what the rules say, I'm (the ref) going to give a yellow because giving a red is too harsh for what the foul was. Simple as that.
Like when you see contact in the box that the ref lets go, whereas if the same contact happened out in midfield it gets called 11 out of 10 times. Sometimes refs use a little discretion when deciding how strictly to apply the rules.
Getting back to Lawrence, I love the guy and think he had a great game, but he went a little overboard when he screamed in Villalba's face. Lawrence is generally a pretty cool character on the field, but he let his emotions get the best of him there. If the game wasn't basically over, he maybe gets a stupid yellow, for the antics after the tackle rather than for the tackle itself.
Then you are just making up rules and shouldn't be a ref. Its like saying "that goal was completely against the run of play, they didn't deserve it, so I'm going to disallow it."
A yellow in that situation is simply not an option available to a ref. There are situations when refs have discretion, and situations where they don't. This is one where they don't.
I absolutely love Kemar as a player, but I don't think he's the brightest bulb and things like this are why he doesn't deserve the captains armband.
"Everybody has a plan until they get punched in the mouth." - Iron Mike
Bitch covered my plaid?
The sorrow inside me grows.
I need my plaid pitch.
"It goes without saying that when things don't go your way they just don't go your way. " - JCO
"He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right.”
George Best, on David Beckham