Its not particularly difficult to do but clearing out the blacklist is just another inconvenience on a player whom already has been harassed by this problem. We pay for a service and shouldn't have to be bombarded by advertisements. I know gold selling and whatever scheming ways they go about trying to drum up business within the game is something that will never go away but SE should give us more tools to protect our privacy and peace in good faith. Instant reporting function, white-list only message option, flagging names as banned as mentioned above are some of the things which could help and I wish were made available to us.

As an aside, I find it silly that tells are blocked during certain content such as dungeons to "prevent players from being harassed" yet it seems perfectly acceptable that we be harassed with them doing literally anything else.