Well, if we're going to exchange recommend viewing material, I might recommend this one by Adam Curtis:
checked it out. watched every second, wasn't quite sure how the discussion of positive liberty and negative liberty related to your original subject matter of
"I was having a discussion with a friend of mine about the role of the state in shaping society. I proposed that increased social programs funded by the taxpayer can work to prevent disenfranchisement and ghettoisation and so rise the 'baseline' of society which in turn benefits everyone eventually"
but by minute 59:00 of the video when the end statements swung back to postive liberty then i figured out where your coming from. i think very unsurely.
i believe that state government should be the representative of its people and the federal government is the agent for the states. neither the state nor federal governments play a role in shaping society as they mearly reflect their constituents and do not shape their constituents. the people can work to prevent disenfranchisement for other people. your question was "is it ethical to resume "the experiment" ". i don't know that i can answer that because i'm not sure i understand what you think the "experiment" entails. if you think the "experiment" entails the theory of negative liberty with the inclusion of force to spread the idea of liberty then the "experiment" should not be resumed. if you think the "experiment" entails the theory of positive liberty then the "experiment" should not be resumed. if you think the "experiment" entails the theory of negative liberty without the use of force to spread the idea of liberty then yes the "experiment" should be resumed.
you make the statement that ""The Great Experiment" of the USA has worked, there's no denying that". i'd have to disagree if it entails the use of force to spread liberty. it has only been in the most recent of the 200+ year history that the USA has used force beyond defensive force on such a large scale to try and create a pocket of liberty in the middle of a zone without. it has only been in the most recent of the 200+ year history that the USA has gotten away from individual liberty and leaned torward an inverted model where the federal government is at the top of the hierarchy, states below that, local governments below that, the people on the bottom (the reality is the hierarchy isn't quite there yet but sure seems to be getting close to it). we do not need to resume the "experiment" if this is part of the "experiment". the hierarchy should always be the people at the top, local government representatives, state government representatives, and the federal government who works for the state governments as an agent representative. as such only the people have the true power to shape society. it is up to people to help people.