Stupidity: There's no reason whatsoever for Mr. Walker to trash the other rooms of David's partners. Someone as tough-minded as Mr. Walker would have been able to recognize the consequences of his behavior. He could have simply trashed David's room and let it be. It simply seems like a plot device to justify David's gang attacking the Walker residence.
Stupidity: In real life, David beating Gary would be a very big deal since it happened in front of many witnessed and on school property. He would at the very least be arrested or detained sooner or later, if not immediately, for things like assault and possibly reckless endangerment, and could very well have a lawsuit filed against him.
Answer: Not enough information was revealed in the short scene to make any conclusions and there was no concrete evidence that a (dog-related) crime was being committed. There was not even any indication that a dog was present. One might GUESS that David and his friends prepared dogs for illegal dog-fighting or trained dogs to be dangerous, aggressive watch (or "attack") dogs, but there is no proof. "We're here to see a man about a dog" may sound suspicious or shady, but could mean something as innocent as looking for a lost pet. [00:38:36]. There is a second "clue" much later in the movie when Mr. Walker is talking on the phone: "They're running their own cartel and you can't do a goddamn thing about it"? Mr. Walker probably saw some evidence when he broke into their house. While it might be assumed he means a drug cartel, not all cartels are drug-related. But, relating this scene to the earlier one, it appears "We're here to see a man about a dog" is the code for wanting to buy drugs. (The man who answered the door replied, "Does this look like a kennel?") David and his friends/gang appear to have been selling drugs out of their home. [01:15:55].
KeyZOid