Your presumption that legislating on the basis of the "least biased interpretation of the the most robust data sets available" will avoid, or even minimise, the cataclysmic results of such decisions is itself flawed.
Firstly, all the information we have, even if interpreted without any bias at all, is only a subset of all the information there is to have. We do not know how large a proportion. It is reasonable to believe that all the information we do not have outweighs all the information we have and so making decisions based on the information we have is no guarantee that those decisions will be any more right than random, in the long term.
Secondly, whilst you could theoretically (if not practically) eliminate bias in the interpretation of this data, you could not undo the biases in the investigation of the data in the first place. The things scientists have chosen to investigate are the result of their biases, both personal and societal. As a consequence this sub-set of all the data there is that we currently know will not only be definitely incomplete, but will also be a biased selection of all the information there is to know.
Thirdly, no rationality could provide us with the values we assign to competing objectives and this valuing activity is essential to the making of any decision. An unbiased interpretation of data might provide us with with an accurate assessment of the efficacy of a range of strategies where they compete for the same objective, but it would never provide us with any information about which objective to attempt to achieve where two compete. A simple and classic example is the degree of hyperbolic discounting one should apply to the value of happiness now against happiness in the future where the two compete.
Fourthly, legislation is inevitably the result of the human population it legislates, in democratic societies, this is a direct and peaceful relationship at the polls, but even in autocratic societies this relationship still persists albeit a staccato of violent uprisings. No amount of legislation can make a mass of people behave in a way they do not wish to behave for very long (on an historical timescale). There will eventually be a rebellion against any attempt to impose such decisions.
Finally, the human world is incredibly complex because we have so many potential interactions, complex systems tend towards chaotic patterns where small errors can have staggeringly large consequences. Attempting too much social or economic engineering on the basis of the science we currently have would be akin to attempting to improve the entire technology of the mission to Mars on the basis that we know what a diode does.