Redlisting does not involve blacklisting or whitelisting coins. Think of it as attaching a breadcrumb trail to coins that someone suspects are illicitly gained. It doesn't stop anyone from accepting them or spending them. It does, however, provide kind of an informational bread crumb trail for law enforcement to later track if it's necessary.
If I sell something and get redlisted coins for it, then the bread crumb trail leads to
me. I sure as hell wouldn't accept coins that could lead law enforcement to my doorstep, and nobody else wants law enforcement harassing them because they're suspected of being illicitly gained. Therefore, everyone will refuse to accept redlisted coins as soon as law enforcement starts getting search warrants against people who end up with them.
To keep bitcoins fungible and valuable everyone with a stake in bitcoin should accept and redistribute tainted coins as much as possible, e.g. using CoinJoin. When everything is tainted, nothing is.