Morality is not arbitrary in the sense that you can't escape the consequences of what ethics you choose. Ultimately morality has to be based on an objective standard.
And as far as there is no standard definition of the nature of man, that's the most ridiculous. First man is a concept and concrete that exist within the metaphysical universe and is bound by his nature. A man can't fly with his arms, a man can't instinctively know where north or south is without using his reason. there is much more.
To claim that man's nature is socially constructed is to imply that that consciousness precedes existence. Well you can believe what you want to believe, that's fine. And a man who is 400 lbs and eats cheeseburger daily might think he's eating morally but he will suffer the consequences of his actions. So yes morality is subjective in the sense that man has "free will" to choose and shape his morality, but ultimately it has to be based on an objective standard if man wishes to live, because the single purpose of morality is to show man how to live on earth. Or else, why would someone who doesn't want to live, or wants to commit suicide need a code of ethics? why would animals need a code of ethics if they are wired for survival and their will is constricted to non existent. A beaver doesn't wake up and decide, "I'm not going to build a damn, fuck my nature". but many of us do decide to evade reality, our nature, and we do face consequences which do lead to death.
On to the question of govt..
Since i've already explained the need for govt to be based on the nature of man as being a "free willed" "rationally capable" human being, then the task is for govt, if it chooses to be moral must be constructed to allow for the men in that society to operate freely, and to choose their way of survival through reason as rational beings so long as they don't infringe on others.
As far as controls. Having govt agencies that regulate industry is a recipe not for consumer freedom but for monopoly privelege. Just look at how many Monsanto, Haliburton, X sundry business has had the privelege to sit in influential areas in govt in order to influence govt to write regulation for their favor.
If you want to talk about track record, look at the regulation of education, healthcare, and other areas. The record shows decline, not progress.
Facts, and morality are not on your side.