I wish that there was some sort of Internet-wide 'reputation system' that would accumulate one's reputation across all websites they use - while preserving their pseudonymity on each site.
As an analogy, Steam and Battle.net and other gaming platforms have something going for them, maybe by accident: by using one account across lots of games, the risks incurred by cheating are amplified. If you cheat (or harass) in one game, your account can be banned across all games. This means that if you care about your account on one game still existing, you're disincentivized from cheating in other games, even if you don't care about them.
I play League of Legends regularly, and Riot Games has put in huge amounts of work in figuring out a way to discipline abusive players that will actually induce them to reform. They have shown that most people, when branded as abusive, will often reform their behavior immediately - as if they did not realize (or did not internalize) what kind of person they were being. See, for example, http://www.polygon.com/2015/1/6/7500045/riot-games-league-of... . But it's saddening that all of Riot's work in reforming players or banning them if they can't get along with others cannot be used to weed out these toxic players in other games. I love gaming, but, for me, the absolute worst thing about this hobby is how awful everyone is to each other, and I would love to see a systematic solution.
I wish something like Steam's centralized identity existed across online forums. I wish we used one account everywhere, and the use of a widely-connected account was required to sign up to things - but the details of who you are, and how to associate your identity on one site with your identity on another site, is totally masked to everyone. Site owners and users cannot tell that userA on reddit is also userA on, say, some Disqus blog. But your reputation would still be preserved across sites: if you were reported as a spammer or a bully or a cheater on one site, it would be visible to the other sites you were on. And if those sites wanted to ban you based on your common reputation, they could.
This puts a large burden on the identity management platform. They have to handle everyone's privacy and security, deal with accounts being hacked and used for spam or abuse, provide mechanisms for people to prove their behavior has improved and remove black marks from their records, deal with websites that submit false abuse claims, etc. And (hopefully) they have to be resilient to law enforcement trying to use these records to complete expose users on every website. But at least they could do it in one place, instead of every website having to solve all of these problems independently.
It seems to me that good behavior in 'tribal' human society was enforced by having to, well, remain in one's tribe, and having to convince everyone to put up with you if you want to survive. It also seems that being labeled, with numbers, as a 'bully' or a 'cheater' can have a positive effect in reforming people's behavior. We would need a centralized reputation system like what I've described to do this.
This is on the list of "things I would like to build".
[edited for awkward phrasing]