First no single entity has any feduciary responsibility for the blockchain, everyone is either holding stake or isn't, those with stake cannot be said to have such a role over the blockchain but what can be suggested is that in safeguarding their stake/investment they are incentivized to maintain such a role, although indirectly. I wouldn't call it 'let's try it and see what happens' but frankly that is exactly how science of all manners is conducted. The hypothesis is clear: free downvotes will lead to people using the downvotes to combat abuse and encourage self policing, we are trying to see what free downvotes would do and why they would work is very sound and well reasoned: at the moment it make no sense for individuals to spend their resources on fighting abuse when they could focus them on endlessly more rewarding things.
Flag wars, much like self voting cannot be countered through code changes. This has been considered probably from before steem was even a solid idea and AFAIK there has not been any code changes that were suggested that weren't mere hurdles and caused negative behavior to be more obscure and thus harder to detect and that much more difficult to combat.
We don't have any evidence because we have no experience, to gain experience we must try things, we might brake them but we will always learn, regardless if it's a poor decision or a good one, but if we don't try, if we don't take the leap, we won't know.
RE: Downvote Pool Deep Dive