I could be wrong but that is my assumption, that the facility to block a user was one of the benefits of paid membership.
If it IS free then it would not stop my paying for membership of the DP. I believe that it is a very useful website and is getting better all the time.
"Jesus answered them: 'Truly, truly, I say to you, everyone who commits sin is a slave to sin. The slave does not remain in the house forever; the son remains forever. So if the Son sets you free, you will be free indeed.'" (John 8:34-36)