Lets ask Jon about this one. How does linguistics help us to understand human behavior?
There are more fields in linguistics than one. And depending on your definition of 'human behavior', various studies in linguistics can offer different understandings of that behavior.
But I am not sure that really addresses what you quoted from Crash. Astronomy and meteorology, for example, are both agreed to be solid science... neither offer anything in the way of understanding human behavior.
So let's deal with what Crash actually was talking about: Whether linguistics is a real science or not.
The answer, once again, depends on what areas of linguistics you are talking about. Measuring sound waves is clearly a very 'hard-science' activity. Getting fat-paid by MIT to invent nonsense 'theories' about goofy things called Universal Grammar, on the other hand, is as far from science as dogs taking shits.
Jon
Love your enemies!