"Nobody really expects the cops to sweep the dorms at NYU for marijuana, even though this would probably turn up a ton of arrests."
Switch out "NYU" with "ghetto" and your statement is instantly absurd. These laws you're sleaking of are intended to be enforced, selectively. This is HN, we all love statistics. What is the probability that a person standing trial for possession marijuana who was apprehended in their home and where the primary reason provided in seeking the exercised warrant or reasoning provided explaining exigent circumstances was suspicion of possession or use of marijuana and the person on trial is white? Black?
You can't be evidence based when it suits your world view, but not when it doesn't. The term for that is confirmation bias.