Who first said, "You can't legislate morality," and in what context?

What then is the relation of law to morality? Law cannot prescribe morality, it can prescribe only external actions and therefore it should prescribe only those actions whose mere fulfillment, from whatever motive, the state adjudges to be conducive to welfare. What actions are these? Obviously such actions as promote the physical and social conditions requisite for the expression and development of free—or moral—personality.... Law does not and cannot cover all the ground of morality. To turn all moral obligations into legal obligations would be to destroy morality. Happily it is impossible. No code of law can envisage the myriad changing situations that determine moral obligations. Moreover, there must be one legal code for all, but moral codes vary as much as the individual characters of which they are the expression. To legislate against the moral codes of one’s fellows is a very grave act, requiring for its justification the most indubitable and universally admitted of social gains, for it is to steal their moral codes, to suppress their characters.
ATTRIBUTION: R.M. MacIver (1882–1970), Scottish sociologist, educator. The Modern State, ch. 5, Oxford University Press (1926).

https://books.google.com/books?id=pwp-CgAAQBAJ&pg=PT118&lpg=PT118&dq=R.M.+MAcIver+morality&source=bl&ots=zehfR36hZG&sig=dfstM31dDqvF5TVD9Iqqxf4yR0U&hl=en&sa=X&ved=0ahUKEwjYn5mrst3OAhWDCMAKHWl-AbcQ6AEISzAG#v=onepage&q=R.M.%20MAcIver%20morality&f=false

Thank you, elburcher! I admit this once to asking for help with my homework... You exceeded my expectations.

This phrase is so often used in the context of the sexual revolution we forget it was used during the civil rights movement of the 60's, which is the answer I was expecting.

Can anyone tell me if it was Barry Goldwater or Martin Luther King, Jr., who first used the phrase in regard to race relations?

"....he believed that this act unconstitutionally extended the federal government's commerce power to private citizens in its drive to 'legislate morality'....
https://en.wikipedia.org/wiki/Barry_Goldwater

"It may be true that morality cannot be legislated, but behavior can be regulated."
http://news.cornellcollege.edu/dr-martin-luther-kings-visit-to-cornell-college/

This may be impossible, since they both tossed it around a bit. They were saying and writing it in 1963-1964.