Why can we not use Radke et al.'s study to explain the actions of a serial killer who murders innocent victims?
Radke et al.'s experiment measures testosterone's activity in the brain in response to social threat - the angry face - and when we're motivated to deal with that threat. In the serial killer scenario, if someone is innocent they're unlikely to be a threat to the killer - in other words, the murder is unprovoked.
Why should students should learn about criminology?
Because we all have the responsibility to act in ways that will improve society, so if you can learn how to reduce violence when you get older (e.g. by being good parents and voting for politicians who want to improve prison systems) we can all make the future a better place to live in.