Would it be beneficial to take classes on human behavior and psychology for a career in national intelligence and national security?

Yes absolutely. You have already figured out one of the most important things: threats are really about the people. If you don't understand the people doing the attackers or their targets, technology alone will not help. In this article http://www.prnewswire.com/news-releases/cybersecurity-industry-fighting-the-wrong-battle-for-20-yearsnew-research-300250459.html
the quote: "In the more than 2,500 data breaches I have investigated, I can count exactly zero that were caused by non-human-initiated system failure—like it or not, people are the problem," says it best - understanding the system won't necessarily help you understand the human.

Hi Casey, I am not working in the industries you list myself but I am sure that psychology and similar subjects would be beneficial for this type of work. You say that the threats may come from other countries but of course that is not exclusively true - many people with threatening ideas / ideologies can live in our own communities too. A big part of threat understanding and analysis is to figure out how people think and how they would respond to law enforcement actions; so I am confident that the subjects you list would be a great support to your career goals, as well as providing you with many options if you later want to change your direction.
Good luck with you studies - Vee

Yes, indeed. Whether you are in the field as an "operative" or sitting behind a desk analyzing video and audio recordings of surveillance, you need to understand people, their motives, their personalities in order to make educated guess about what is not seen on those video or heard on the audio recordings.