The proposition is sound, but an Open Theist would need the above proved. If however you meant "Let's say that nobody debated that God was omniscient..."If God is omniscient which He is,
"...then would men be able to be Open Theists?" ...could be meaningfully answered. The answer would be 'no.' I believe from a physics standpoint (all created things) that we can show that " God knows all things knowable" (Open Theist paradigm given as true), necessarily applies to all created things, if Einstein's theory is consistently true (E=mc2). If we could/can show Peter meant "everything" literally when he said "all things," John 21:17 (perhaps quoting Psalm 139:1-6) we could prove omniscience from scripture (among other scripture considerations).why do men believe in Open Theism
I do believe there is an onus, upon me, to show why I believe they do teach exactly that. A few scriptures do come to mind (listed in thread now). Foreknowledge is another: the 'literal' meaning is "knows" (not implication - 'knows' implicitly) "beforehand." It is at least strong evidence for the proposition. The immediate verse following John 21:18 is a revelation of foreknowledge regarding Peter's end of life. If there were any qualification we could infer, we'd truly want to see it in scripture: some incredibly pedantic expiation of 'all things that "I" can actually know.' The only thing we have that would even call us to question, would be "Adam where are you?" as if God didn't know.
While one and the other (Omniscience vs. limited) have implications that can assault our theology understanding, I've reckoned that the Open paradigm does more damage to what I expect to be Biblically true as well as doesn't ring true with all of scripture. While it may seem "Adam, where are you?" is damaged by omniscience, it is ever my understanding that God uses scriptures instructionally for 'my' (all men) understanding, thus does anthropomorphize language to us. He didn't ever need to 'come down.' If you follow: God could have sent an angel. It is always, rather, because the men (Adam, Lot) needed God's interaction. It necessitates that we realize God came not to 'find out' but 'to interact.' I do see dilemma, in that "If not I will know" implies His reason (not clearly stated) for 'coming down,' but that is rather an implication. Reading the rest of Genesis 18, we get the sense that both Abraham and God knew how many were righteous. Sodom and Gomorrah were not spared.