The simplistic solution to "have everyone ban non Verified" simply won't work.
Not unless the Lindens do it at the same time.
Let's say every Player who owns land in the Magenta sim bans all non-verified Players from their land. There is still a Linden-owned river running through that sim. The griefers can just stand there and can still do attacks that will lag the sim so much it is useless.
Or they can stand in Maroon, the next sim over, and can do it there. Or in some public sandbox that you never heard of.
Even if you own a private island, and only allow your chosen list of trusted friends to enter the sim, an attack like the one last night that brings down the whole grid brings you down too.
As long as these griefers can keep coming back in 5 minutes or less with a new, untracable account, this hell will not end.
The problem is not that accounts are free. The problem is that accounts are completely anonymous and disposable.
Making a person accountable for their actions does NOT have to involve paying money, or providing a credit card. But it DOES involve making at least SOME effort on LL's part to obtain and have on file SOME sort of verification that they know who the account holder is, and that the account holder is of age.
Right now, if they can't think of any better way to do it, I'd prefer a registration process that had to be completed by postal mail, with photocopies of legal ID, and the new account is not activated until they recieve an activation code by return postal mail to the address that they provided. Will that slow down legitimate account creation? Certainly. But it will completely eliminate the 5 minute script kiddies that come here only to grief.
Make a "demo grid" for anyone who wants to try SL for free and without providing ID. The currency there and the assets and accounts there are completely non-transferrable to the real grid, and they get a stipend so they have play-money to play with. When they want a real account, they have to provide real ID, and make a new account.
But for the mani grid? Lock every damned account out until they provide a verifiable identity. I don't care if that means the grid is a ghost town for a month, while people mail in photo ID, or fax in copies of their ID. It would be worth it to be assured that EVERY PLAYER in the main grid is of legal age and has provided some sort of ID that LL can use to track them down to their home and prosecute them if they crash the grid.