I do not like to use the blacklist feature. It is a last resort measure for me, and one which is or can be ineffectual, besides. I will characterise the problem as concisely as I can manage.
The Blacklist has a limit of 200 names. If you elect to add someone to your Blacklist, it adds only that character - but each Player may have as many as 40 different characters. There are two problems I have with this.
First, the limit of two hundred is too small for a critically-acclaimed MMO that boasts having millions of people who log in daily to partake of the content. Second, if a player is dead-set on harassment of you, you will end up needing to blacklist the same single person 40 times. At that point, 20% of your blacklist limit is literally one person.
To be clear, I think it is wonderful that we are allowed 40 characters. I wouldn't mind if we were allowed to have literally 8 characters on every server world in every region all across the entire game. That's not the problem. The problem is that when you blacklist someone, the feature should functionally blacklist every character on the account of that individual.
Additionally, the blacklist feature can be circumvented. I have had numerous occasions on whence someone on my blacklist ended up in the same roulette as me. The reason for this: the blacklisted person was partied up with someone who was not on my blacklist and who had similarly not blacklisted me. When this happens, I try to remain calm and friendly, and perform the role I queued up for appropriately, anyway. I don't punish someone because I happen to have a friend of theirs on my blacklist. It isn't their fault I blacklisted their pal.
In a similar vein, I would like to also mention shortcomings in the Friends List. First off, the limit of 200 names, and the failure to add the account and not individual character. Second, the inability to enter a personal note about the person so that I remember them, which would be more important if the former problem were rectified. I have one friend who has sent me a friend request four times on four separate characters on their character list. This wouldn't be needed if friendships were player-to-player, not character-to-character - which is where a player-written note would be important.
Additionally, friendships in the game can be ephemeral. It's in the nature of people to grow close or apart, particularly on a video game if you are not doing a lot of content together. As a resolution, I would like it a lot if, when I remove someone from my friends list, it would also remove me from their friends list - and vice versa. This is a pretty common feature in most social media, friend lists are rarely one-sided, and I think that's how it ought to be.