I've got an idea:

There should be a faster alternative way of becoming a member (for those who do not want to spend 4 hours and write 5 posts).

For example, a newbie could donate 0.01 btc and automatically become a member.

Or he/she could make a deposit of 0.1 btc (which would automatically returned to her/him after she/he publishes N useful posts and spends M hours online).

I don't think trolls are ready to pay/risk their money.