Currently within every state aside from California, it is a legal defense for murder and assault to say a person was unaware of the victim being Transgender. This has allowed a fair share of murders and countless assaults that are premeditated but later claimed to be crimes of self-defense to go under the radar or earn a lesser sentence.
By enforcing a legal ban on this defense you guarantee that when a Transgender person is murdered they are treated with the same respect that any other victim to homicide is treated.