I think it comes from your confusing of desire, will, and nature on man's part, and those same things when in reference to God. Arminians tend to view God in human terms, i.e. as just a bigger version of ourselves, rather than understanding that He is totally other than what we are. We were created in His image, but that doesn't mean that we are like Him or He like us. That is proven by the fact that God, in the person of His Son, Jesus, had to become a human in order to redeem us.
Any time a Calvinist says that sin is a part of God's Plan, Arminians immediately say that we are saying God created sin, and is the author of sin. That is a red herring they draw out to deflect the truth. Their man-centered, Gnostic view is that man screwed up God's Plan, so God has had to do all sorts of things to try to win man back to Him. They put man at the center, and man's will as the deciding factor, and make God a reactionary Being, reacting to man's decisions, man's desires. It all would have been so much better if man hadn't sinned....They've got God doing damage control.
The truth of the matter is that if God is Omnipotent, Omniscient, and Omnipresent, then anything that happens (has happened, will happen) in His creation is foreknown, fore-planned, and fore-ordained. How could it not be, given God's obvious attributes?
Sorry, I'm not reading any further. You don't know what you're talking about.