This is not true, (or if it is being taught, the professor doesn't understand what he is supposed to be teaching.) What first year economics courses do teach--what is meant by the term 'homoeconomicus'--is that in aggregate, people rationally pursue their own self interest. 'Self-interest' is defined here as a subjective utility threshold. So, for example, if someone cares about their children, they will work hard and make a lot of sacrifices to support their children. The idea is that the market follows the aggregate self interest of people and so we don't have to worry about the miss-pricing of goods because the market will take care of that.

The difficulty with this idea isn't that people have wrong values--modern economics presupposes that values are inherently subjective and thus cannot be judged--it's that people are capable of making consistently rational decisions in pursuit of their subjective goals despite information disparities and cognitive biases.