Most law suits aren't due to breaches of the law, but breaches of contract. Whether terms of service constitute an enforceable contact is another matter.
Nope, it's not a settled question in the way that I think you mean. Each ToS is different so each would be subject to individual legal analysis in court on its own terms.
Questions would include whether the ToS is unconscionable, whether the terms violate laws of the locality/nation, and so forth.
It's the same with traditional contracts - the fact that contracts have been around for hundreds (maybe thousands) of years doesn't mean much if you and I create a brand new one between us. Our contract's specific terms (and events/actions between us as a result) would be the issue in court.
Why can't FB simply include a clause like "No kind of automated scraping is allowed, except for search engines in robots.txt"? This would save them so much time in court, arguing over the use of fake accounts which should really be irrelevant.
It's not clear that clause would be enforceable. Scraping has been found to be lawful in many jurisdictions, including the US, even without the consent of the host.
Congress or a state legislature could pass a law that says "No terms of service are ever enforceable" but to my knowledge no one has done that.
So, under the current state of the law whether or not a contract is enforceable depends entirely on what the terms in that specific contract are.
Unfortunately, this is yet another instance where the law has failed to keep up with technology. Contract laws (at least in the USA) date back long before anyone ever dreamed up the idea of a EULA or ToS. Our laws contemplate two or more parties with roughly equal bargaining power sitting down and hashing things out, and go from there.
Laws based on that assumption are a pretty poor fit for a world filled with EULAs and ToS but it's what we are stuck with at the moment.
Probably should also add "successfully", there's a reason NYPD had/has guns that require 12 pounds of force to pull the trigger (instead of a normal ~5 lbs).
Software that exclusively has illegitimate uses has been shut down. Whether we agree that it is a good argument or not, it is definitely an argument people have made (that some types of guns are mainly designed to hurt people).
With software of course it is a little complicated because:
* it can be produced really easily in a distributed fashion over the internet by anonymous people in many jurisdictions, so there isn't always an obvious company or entity to sue
* most automation tools can be repurposed for malicious use (nobody would sue John Deere because their tractors can be armored and turned into pseudo-tank things)
