And which "competing systems" would you have them teach? Economics isn't a course on various forms of government, they were teaching you how the system you lived under actually operates.
We don't actually live in a purely capitalist society. Patents & copyrights are embedded into our constitution and are anti capitalist in that they create a monopoly based on the force of law rather than a free market.
Utility monopolies in areas - ie cable, telephone, power
Emergency medicine is absolutely not a free market item - nobody does research and decides which hospital to go to for their heart attack based on cost/benefit ratios.
Even back to the 1700 & 1800s, there have been consumer protection laws in effect that curtail the ability of businesses to market and sell products - thankfully we no longer have lollipops flavored with horse piss.