Grammarian has already pointed out your historical astigmatism in asserting that the Puritan John Milton was an "Arminian heretic", but I personally love the fact that you now credit Milton with the founding of Open Theism, a view which was not to surface until 300 years after his death. Some guy, that Milton.
But I'm certainly happy that you won't let a little history get in the way of your varsity name-calling routine. After all, how could one possibly defend the vicious construct if he were to be deprived of his name-calling 'tools'?
You know me, winston. I always revel in correcting historical error! This case is no different.
"Open Theism" is not new at all. It's simply a renaming of an old heresy, Socinianism.
The Socinians, however, and some of the Remonstrants, unable to reconcile this foreknowledge with human liberty, deny that free acts can be foreknown. As the omnipotence of God is his ability to do whatever is possible, so his omniscience is his knowledge of everything knowable. But as free acts are in their nature uncertain, as they may or may not be, they cannot be known before they occur. Such is the argument of Socinus. This whole difficulty arises out of the assumption that contingency is essential to free agency. If an act may be certain as to its occurrence, and yet free as to the mode of its occurrence, the difficulty vanishes. That free acts may be absolutely certain, is plain, because they have in a multitude of cases been predicted. It was certain that the acts of Christ would be holy, yet they were free. The continued holiness of the saints in heaven is certain, and yet they are perfectly free. The foreknowledge of God is inconsistent with a false theory of free agency, but not with the true doctrine on that subject.
Charles Hodge, Systematic Theology, I.5.8.D
Socinianism, of course was a heretical spliner group during the Reformation period (that means 50 to 75 years before Milton was born, if your name starts with a 'W'.)
OP, perhaps you can look into Milton's and/or Ralston's potential flirtation with Unitarianism (which Socinianism was the precursor to).
I'd look into it, but I am to take my daughter to the "Carousel Mall" shortly!
Jean