No one is complaining about Telegram, which requires a phone number, or IRC, which can reveal your IP address.
Anyways, it's not like they have any illusions about what Discord is:
>arisuchan.jp has a presence in a variety of services including an IRC channel and Telegram chatroom in addition to this Discord server. I'd like to take this opportunity to remind you that Discord is a centralized service that in all likelihood actively data mines its userbase as their ToS permits.
>Please take all sensitive communications as needed to secure channels (e.g., XMPP/OTR) rather than posting any sensitive information in Discord servers or direct messages. We'd much prefer a libre alternative to Discord with many of the same bells and whistles, but Discord is ubiquitous, convenient, and hard to avoid if you have many friends spread across a lot of online communities who may not be knowledgeable when it comes to privacy and mass surveillance.
>Never install any piece of software, proprietary or otherwise, that you believe could put you at risk. If you must use this software, remember that everything you post is stored on a server to which you have no real access. This is our official stance, but we use this Discord community as-is for casual discussion and anything non-sensitive.