If the member never does any of the above, that means the member ought not to pay for any evil. Because it can be said, the member is not gaining anything from the forum save knowledge.
He is not gaining anything in a monetary sense, but he still gets a lot. Like you said, he gains knowledge. Users also get help and advice if they ask for it. They can take part in discussions, get merits and merit others. Getting rid of the evil fee would be the best thing to do. Instead, scammers and scamming should be strictly forbidden. Scammers should be banned to make the marketplace and overall forum experience better for everyone.