The Unban requests fall short:
Unban requests are great for the person being banned to have the last word.
Why can't mods reply back to the banned?
The person could have been banned by a part-time mod and I have no idea of the details and therefore cannot assist making the unban request moot.
All viewer chat transcripts should remain accessible by mods at all times. Even when the said viewer isn't in chat, banned or when the stream is no longer online.
If the username is spelled correctly the mod or broadcaster should have access to their chat records to support their argument.