[mrngm]

At least under GDPR, collecting personal data is already considered processing. Processing is only allowed under specific conditions and purpose.

It would be perfectly fine if Discord stored messages from users (for brevity, assuming that's personal data), made it searchable and available as long as the user exists on the platform, provided that they specify this as the purpose of processing, and the user explicitly gave informed consent. Should Discord want to perform any other processing besides that designated purpose, they would (again) have to receive the user's explicit, informed consent. Otherwise, it's simply not allowed.

No need to remove messages in such a case. Of course, technically they could process that data for a different purpose than specified, but that's illegal and may eventually result in a fine that can be based on a percentage of total global revenue.

Not profit or loss, revenue. Then suddenly it becomes a really interesting business decision to do other than defined things with the data at hand.

(and something something purpose limitation, data minimization etc.)