What sort of legislation could be put into place that would effectively prevent these sorts of situations without having horrible side effects?
2. Mandate that each accused has the right to face their accuser - this means each ban must provide a way to speak to a person via phone and email to appeal it.
3. Mandate that each accused has a right to a fair trial - this means that, at some point in the appeals process, the banned must have the option of, with minimal investment of time and effort, being judged by a neutral party, which has the power to ultimately overturn judgements by the non-neutral party (Facebook)
The problem isn't that there are no solutions - each of these three totally reasonable rights was conceived of centuries ago. The problem is that Google doesn't want to do them because it is at least 1 cent cheaper to _not_ do then.