I didn't necessarily agree with Barkley's comments, or the timing of them, but I do agree with the idea that a big part of the NBA game is having some at ude. Which is basically the point Barkley was really trying to get across.
Dirk too easily allows opposing players to "punk" him. Whether it's Shaq putting an elbow in his grill in the Finals, David West tapping his face, K-Mart putting a flagrant on him, the entire Golden State fiasco.....Dirk just takes getting on while offering no resistance whatsoever. You can't have that type of softness and expect to be a true leader in the NBA.
Obviously Dirk shouldn't go all Ron Artest when an opposing player tries to punk him, but he's gotta show some backbone. Get in the guy's face, call him a mother er, make sure that he knows not to try and pull that again.
And since Dirk is the leader, that type of soft at ude trickles down to the rest of the team. That's why the rest of the team will let snowball on them during games, that's why complete meltdowns happen so often for the Mavs.