If you provide Terms of Service (TOS), are you ethically or legally obligated to enforce them? Let's look at the Twitter TOS controversy, from a simple, common sense point of view.
Ariel Waldman is a Twitter user. She complained to Twitter about another user who was harassing her on Twitter. This was beyond mere disagreement or a casual "you're nuts" type comment. The harassment involved filthy language.
Twitter, not known for being open to user requests and suggestions, not only did not enforce their own Terms of Service. They also shamed the victim, whined about their small staff, and declared they were "offended" at the victim accusing them of not caring about users.
This is not the proper way for a company to respond.
Some relevant items from Twitter's Terms of Service (due to change soon):
4. You must not abuse, harass, threaten, impersonate or intimidate other Twitter users.
Violation of any of these agreements will result in the termination of your Twitter.com account.
While Twitter.com prohibits such conduct and content on its site, you understand and agree that Twitter cannot be responsible for the Content posted on its web site and you nonetheless may be exposed to such materials and that you use the Twitter.com service at your own risk.
Did Twitter stand true to their TOS, and account removal policy, in Ariel's case, or were they negligent?
Here's the TOS / Ariel Waldman debate on the Twitter blog.
More here: Summize archive re: Ariel.
And here: Twitter refuses to uphold Terms of Service.
It's not "mediating disputes between people" that's the issue here. It's enforcing your TOS.
You decide if you like Twitter's tone and handling of this situation. Personally, I do not.