I don't think emotional offence should be treated exactly like physical harm. Different people may take offence from different actions, and it's not fair to require everyone to judge accurately what is and what is not offensive to all the other people they're going to interact with, especially in a society that is aiming for diversity. In East Asia, where most people think alike, it's easier to guess people's reaction, but it's definitely not so in other parts of the world.

For physical harm, however, ignorance should not be an excuse. It may reduce the responsibility, but it should not completely remove it. Not knowing something can kill doesn't change the fact that one had actually killed.