You can't argue with a river, it isgoing to flow.You can dam it up†put it to useful purposes†deflect it, but you can't argue with it.

-Acheson, Dean Gooderham
On the fruitlessness of keeping Russian fishermen from waters that should be off limits. Quoted in David S McLellan Dean Acheson: The State DepartmentYears (1976).

I count our progress by the extent to which what we cried in the wilderness five and thirty years ago has now become part of the assumptions of the ordinary man and woman† It is better to argue from what has been done to what may be done, rather than to suggest that very little has been accomplished.

-1st Earl
  Of the Labour Party. Letter to Harold J Laski,1 May.

Argue for your limitations, and sure enough, they're yours.

-Bach, Richard
  Illusions.

The enemies of freedom do not argue; they shout and they shoot.

-Inge,William Ralph
  The End of an  Age, ch.4.

Give me the liberty to know, to utter, and to argue freely according to conscience, above all liberties.

-Milton,John
  Areopagitica: a speech for the liberty of unlicensed printing.