Anonymity
Anonymity is the ability to hide your real identity such that it cannot be differentiated from other identities, meanwhile pseudonymity is the ability to hide your real identity and replacing it with another identity. Throughout this text I will refer to both together as "privacy of identity".
Privacy of identity incentivises dishonesty and inauthenticity. No longer you have to be ashamed for your fuckups and mistakes, because you can just hide them under a fake persona. This is obviously extremely harmful, since it makes people pretend to be somebody they are not, as your fuckups and mistakes are part of you just as your successes and moments of joy. Shii (from "Everything Shii Knows") has refered to this as the "the right to vanish", and if you think about this for longer than a few seconds, you will realize that this is not something society should incentivise; you just ditch your responsbility and pretend like thing you did never happened. The Internet gives you the delusion that you can just earase your most embarassing moments of your life, but in reality they still happpened, you cannot turn time back, all you can do is lie about it, which is pathetic. Obviously, if you give people the option to selectively reveal details about themselves, they will try their best to not reveal stuff they don't want you to know - this obviously is the case without the Internet too, however, the Internet makes this a lot easier. Not only is privacy of identity bad, because it is inauthentic, but also because it is, for similar reasons, dishonest. It creates a discrepancy between what you admit publicly and what you really think in private. Proponents of anonymity pretend like this is in any way good, "Ohhh, you can just speak freely and don't worry what other people think about you. Just express anything you want while hiding behind a pseudonym", yet it never crosses their mind, that it might be a good thing to admit what you think with your actual identity, take accountability for what you are saying, and not have a huge gap between what you admit to thinking publicly, and what you are in private.