For one, because it has been stated by Blues that the moderators have problems tracing patterns in activity back to a singular person for the purposes of applying penalties to forum trolls, because each character you post with is an island in terms of the data. That leads to situations where, like with the T-squad, people repeatedly roll up level 10 characters or Classic alts, start posting with them, delete the character, and while the forum moderators whack-a-mole with their individual post it’s seldom identified as a consistent pattern by a single person.
For two, because if there was a singular posting identity on the forums, you could ignore someone and all of their alts with a single request. Repeat-offender trolls would get frustrated when their posts started getting less traction because people would have already identified that they weren’t posting their genuine thoughts and opinions and pre-emptively ignored them, and gave others a heads-up that the person was a known troll.
For three, because right now each account gets up to about 160 likes and 160 flags on the forums, one for each character. With that, a single person can hide the posts of someone they want to silence by repeatedly reporting it for moderation, and with that they can create the appearance of a consensus, like people switching alts to vote on polls making those polls pretty useless for being a genuine gauge of the popularity of an idea or opinion. When the T-squad was around, they were consistently upvoting their own posts to make their ideas look popular and encouraging an environment where people who didn’t agree with the opinions that they pretended to have felt persecuted and overwhelmed, and flagging people who tried to identify their behavior to others. They played these forums like a fiddle for like a year, causing massive damage to people’s opinions of the groups that they pretended to be a part of.
For four, because it would have a chilling effect on some of the worst of people’s behavior if they do actually play the game and have friends, GMs, family, etc. who wouldn’t approve of their trolling habits and the opinions that they express disconnected from the characters that they know. If they were to switch to a Classic alt just to be like, “Oh yeah, well, women should be in the kitchen anyway, make me a sandwich!” they might end up having their GM, their friends, or their wife raising eyebrows about that. Future GMs, future friends, and future wives could also see that behavior and label it as the behavior of a person that they don’t want to associate with.
A lot goes on on these forums that isn’t necessarily actionable in terms of getting a person’s post deleted and actioned, but is still a trollish, negative, unsavory opinion to express. People are free to express their opinions, they’re even free to pretend to express inflammatory opinions for the sake of being disruptive, mean and negative as long as they’re not breaking the rules of the forum, but they shouldn’t be free of any kind of social consequences for that behavior by tossing a smokebomb and putting on a fake mustache and a top hat to pretend to be someone else.
I personally don’t have a problem with a “singular ID” being some kind of forum identifier instead of a person’s Btag, I just don’t see the point when there’s literally nothing nefarious that you can do with a Btag that you can’t already do better by knowing a person’s character-server. If people want to be super paranoid about it and make Blizzard reinvent a function that’s already built in to the forums, it’s whatevs to me, but at the same time a lot of people claim to have problems with the privacy of their Btag and will make up a million wild stories about what can be done with them when really they just don’t want any kind of accountability for the things that they post to be tied back to them.