That is a fair concern. However, as a customer - searching my message history is a desirable feature. I would rather see meaningful individual and corporate accountability for privacy breaches. The threat of jail and/or 100MM's in fines should motivate better data handling.
Sorry but no, I don't want my messages deleted. I use search history all the time even to search for things I personally said. I can get behind deleting messages if the account is deleted though, but as some type of automatic thing based on time in the past? No thanks.
That you wold chose to 'keep your messages' is a little besides the point of those who would opt for more privacy.
Nobody is making the argument you should be forced to delete your messages.
In any normal world, messages that are not used would be deleted as a matter of privacy. They're kept, because they can be kept, and they can be monetized. That monetization has zero benefit to the user, it's just an artifact of our odd way of doing business where we continue to externalize a lot of things. I think over the next 10 years we might see a regulator shift , which also means costs more directly exposed, meaning Discord may cost $1 month, i.e. the externalization 'costed in' like carbon tax on fuels.