In considering the length of bans, I think its important to consider the possible harm caused. Trolling - its annoying, but not so much. Petty slanging back and forth - a bit more so. Insults and threatening behaviour ... much more so. And the punishment should reflect that.
It is interesting to me as this week in Australia, a media presenter by the name of Charlotte Dawson committed suicide.
She suffered from depression and had various challenges facing her ... but its relevant here because last year she was the target of a bullying/trolling/hate campaign on twitter - which directly led to a suicide attempt that night.
She had quite a large number of people insulting her - using the hashtag #diecharlotte and telling her to go hang herself.
She was a vulnerable person with a mental illness - who was subjected to cyber bullying to the point that she posted "you win xx" and took a bunch of pills.
My point is - you dont know the person on the other end of the computer.
You dont know what state they are in or their vulnerabilities. Using language that can be interpreted as threatening, or repeated cyber bullying can be incredibly harmful to some people. Many will be able to walk away, will just brush it off, or will fight back ...
but some people can not.
Whether its a real threat or just a bit of slanging - if the person on the receiving end is vulnerable, it can do a lot of emotional damage.