Forum posts don't disappear. Why should it matter that chat could (doesn't have to be, but could) be persistent with Discord?
I would also like to second a lot of what Ivien Sedai said here. I manage a Discord server for my WoW guild, and quite a few friends who play League also use the same...
^
What they said. :)
If it's a matter of moderating voice...why would you have to? Is it impossible to just explicitly state moderation would be for text only?