Should ignorance of the law be an excuse for this man? Call me crazy, but it seems to me that those enforcing the law should be much more responsible for knowing it than those who are being oppressed by ignorance of it.
I would add another question along these lines. Why is it acceptable not only that ordinary citizens (particularly members of racial and ethnic minorities) must behave with extreme discretion, and often show humiliating deference, to avoid being abused or arrested when dealing with police, but also that a significant fraction of police are power-abusing bullies with hair-trigger tempers? Call me crazy, but it seems to me that those enforcing the law should be selected for thick skin and the ability to defuse adversarial situations rather than make them worse. Many police behave decently and even admirably, but there are also so many who are hot-headed jerks that it’s obvious that the police culture has systematic management problems.
UPDATE (July 16): Brendan Loy posts an update to his original post.