I've always viewed expiration dates on pharma products as a big company conspiracy theory to get you to throw perfectly good shit to buy some more. My wife buys into it...I don't.
All I know, is that I take 3 year after expiration date Excedrin and it still kills my headache. Same goes for allergy pills and anything else I can think of.
It's not really a conspiracy though.
It's the furthest out a manufacturer is willing to guarantee full potency and effectiveness without complications - sometimes, once it's out of the their hands, and who knows where you keep it, shit can go wrong, and people MAY get hurt. If pills "hurt" you, and they are expired (and they never hurt you before), it's quite likely either completely unconnected to the pills, or something happened that wasn't originally a defect in that batch. The manufacturer shouldn't be responsible, and after such date they are cleared of such in most cases. Of course, just that type of situation is incredibly rare.
But really, like most things, it shifts the "thinking" toward the consumer - if they care to keep abreast of accurate knowledge, cool; if they do not want to think and instead be an ignorant fool, well, cool. Companies aren't really making the dates they do as part of a conspiracy, it's more because dates have to be there, and testing for a decade or longer would be expensive, and thus also likely increases cost to consumer. We may want the former, but we don't want the latter, right?