Two points. When they're looking for drugs, like you say, and they find counterfeit merchandise, should they ignore it? And, it may not be illegal to own or purchase, but smuggling and conspiring to smuggle counterfeit items over international borders is illegal, so unless you're buying them from a bloke down the pub, you're breaking the law.
Why do customs make our lives difficult? Because we're in an illegal hobby and we know it. If they see us while looking for bombs, weapons and drugs, they're not going to ignore us. People, we are smuggling and we should be aware that at the very least we're deliberately avoiding import duty. The sooner we realise we're not the victims here the sooner we'll stop being so complacent about it.