If this became a rampant issue, maybe it would be time to rethink the law? Discretion allows abuse. Laws that are not applied uniformly run counter to the notion of "Rule of Law".
...unless they're black?
There's no reason to give cops this discretion, it just leads to unfair policing practices. Better to have police enforce all laws and think hard about what we want those laws to be.
This is what I was alluding to. Historically judges have had a lot of leeway when it comes to sentencing, and, having heard all the details of the case, they are in the best position to decide the defendant's fate. (For what it's worth, I disagree with mandatory minimum sentencing laws.)
Doesn't overlooking the beer also mean we've decided it's ok for teens to drink? What is the difference you see?
So it really comes down to philosophically purity vs. pragmatism. I'm naturally drawn toward the former, but as I've gotten older I see more value in the latter, even tho intellectual it bothers me.