A couple of comments:
The code uses a non-default prefix for the phplist tables, “pl” instead of “phplist” so that is something else that people would have to change. Also, the “user” prefix is optional so that too might have to be removed before trying to use the script.
It is actually valid for the user_blacklist table to contain rows with email addresses that do not exist in the user table. The recipient of a forwarded campaign, who is not himself a subscriber, can click a link to stop receiving emails from phplist, in effect a non-subscriber blacklisting. To remove such rows is probably “the wrong thing to do”.