Facebook clearly does have a bug here, where they didn't warn the ad buyer that they were excluding an age range. Someone operating in good faith could have one ad for 18-29, another for 31-40, and one for 41 and up. According to the 'outrage' this is highly illegal. But clearly a simple mistake, an off by one error if you would :D. Facebook knows you don't want to excluded anyone, so they should warn about the excluded age range. No matter where it shows up.
Also, is advertising to (demographic) most likely to buy your service really exclusion/discrimination? To the level of a crime? I'm unconvinced I agree it should be.