Knowing is much worse. Not knowing reflects worse on the seller, who misled the person who bought it and passed it off as real.
But when a person knows they are carrying a fake, they are supporting copyright infringement and illegal activity (selling fakes is illegal, and so someone buying one must by default support that activity). They are also trying to make other people think they are someone or something they are not.
People should be proud of who and what they are and not try to put on an act. To carry a fake says, "I think you will respect me more and think I'm a person with more status if you see my bag and think it is real. I am ashamed enough of who I am that I'd rather lie to you than admit who I actually am." And that, to me, is sad.