All of these "bans" seem unnecessary. They sure were when I ran the show here. (I used to run the LPSG, for those who don't know.)
We're all adults. If someone is sending you offensive private messages, why go crying to the mods about it? Just "ban" him (or her) yourself by adding him to your Ignore List. No one has to even know that you've done it, and it would prevent big discussions like this one every time a long-term member is banned or suspended.
If harassing messages are being posted in "public" on the board for everyone to see, that's one thing, but banning or suspending someone for having a squabble with another member in a private message? Give me a break. What is this - kindergarten?