From Cross Theology:

PHILOSOPHICALLY

The reason why I personally became an Open Theist was:
Imagine that God created you as the soul that would eventually become Judas Iskariot, the betrayer. And suppose He created me as the apostle Thomas, who would eventually be a great evangelist in the Far-East.
And imagine that He was completely sure that those events were going to happen. And that you would burn in Hell and I would live in Heaven.

Philosophical problems with Calvinism: Future is settled, human beings have a “free will” to choose to do only evil (= Total Depravity). Leaving one in his sins and the other not, just out of God’s supposed arbitrary choice would make Him a “respecter of persons” (Acts 10:34). God wanting that a big group should perish (2 Peter 3:9, 1 Timothy 2:4-7)

Philosophical problems with Arminianism-like future view*: God bringing those souls into exsistence of whom He knew, they would not turn from their wicked ways. “If God truly does not want anyone to be lost, then why does he create those of whom He knew they would be lost forever?” As in the above example: (the souls of) Judas and Thomas would not have been really free to choose between good and evil. They would not have received an equal chance. Calvinism would have made most sense then.

* View in which God foresaw who would eventually repent and endure and who would not. (I held to that part of the view) And that He only gave the chance to repent to those who would believe.

I did not hold to that part of the view, since, I believe, philosophically, that God needs to have given everyone an equal chance to be able to be righteous (Romans 9:14). For isn’t that required to make a righteous judgment at judgment seat and have the people honestly say: “true and righteous are His judgments” (See Revelation 19:1-2)?