It's stupid and egregious to ban someone for "breaking TOS" or "sharing harmful information" and not telling them exactly what they did and where they did it, no matter what you see them as.
Not only that, you're doing that to satisfy the curiosity of someone you've decided you don't want anywhere near your site. I'd be on board with your line of argument if it involved a payment of $X to cover out-of-pocket expenses and the hassle of dealing with BS.
However in this instance they (Discord) would have no reason to care about what you want, so saying that you want something is really no argument.