Much of the point of having states experiment isn't to get everything right, though, it's to prove that the sky doesn't fall when a new social policy is enacted. Usually whenever any new social contract is proposed, there's an immediate chorus of "this will lead to chaos and anarchy!", and it's only when a policy has been in place for a couple years can people judge whether it really
did lead to chaos and anarchy.
For both gay marriage and marijuana legalization, for example, certain states tried it against a chorus of voices that said "This will lead to the destruction of marriage as we know it" or "crime will go through the roof". And then that didn't happen, and so other states tried it, and eventually it filters up to the federal level.
There have been other cases where policies have been tried that did lead to widespread chaos and negative consequences, like Nebraska's safe-haven law that defined a child as anyone under 18 and led to mother's abandoning their teenagers because they didn't want to deal with them, or California's Prop 8 that was supposed to keep senior citizens in their homes but had the unintended consequence of restricting the supply of housing and driving housing prices through the roof. In these cases, the laws have not been duplicated in other states, at least not without changing the problematic details.
There's talk in a few states of introducing both universal health care and net neutrality as state laws. This will be an interesting experiment, and will let us see whether the sky does in fact fall before rolling it out nationwide.