The scriptures are clear that God desires all men to be saved.
Yes, He desires all people to be saved and to come to the knowledge of the truth (1 Timothy 2:4). But His
will is a different thing altogether. I'll offer this parable... :) A person is trying very hard to lose weight. She really wants (desires) a piece of chocolate cake for dessert, but, her will trumps her desire and she passes up indulging herself with the cake. This is called will power. :) By the same token, God's heartfelt desire is that all would be saved, but not all will be saved; God's justice demands the wages of sin be met -- this is the will of the Father -- and some will bear that burden themselves instead of repenting of their sin, believing in the Lord Jesus Christ and His bearing our burden on our behalf on the cross. As Paul points out in Romans 9:16, it
depends not on human will or exertion, but on God, who has mercy, and God has mercy on whomever He wills, and he hardens whomever He wills. So, there is indeed human (free) will and exertion, but our salvation
depends not on our will or exertion but on God and His mercy.
A sovereign God can allow free will. A sovereign God can know our ultimate choice without making it for us.
Nobody's denying that. We all have free will, and we all have a choice to make, and God's offer of salvation requires us to make a choice. The issue not about choice or whether our choice is free or not. It is about whether we are born again or not,
made alive by the Spirit and thus
enabled to freely choose God. As Jesus tells Nicodemus, the wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes... so it is with everyone who is born of the Spirit (John 3:8). Until that point, we are dead in our sin and cannot choose God... we will not fail to choose against God, because we are not
of God until then. So our choice depends on God's initial work in our hearts -- whether He does that work via His Holy Spirit (or not) and causes us to be, as Peter puts it, born again to a living hope. Paul says in Ephesians 2:8-10 that it is by God's grace that we have been saved through faith, and this is not our own doing, it is the gift of God, not a result of works, so that no one may boast, for we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them. Paul also says that if it is by grace, it is no longer on the basis of works; otherwise grace would no longer be grace (Romans 11:6). Jacobus Arminius, however unwittingly -- as Pelagius did before him -- made faith out to be a work of man rather than the gift of God, and that is antithetical to Scripture.
People are not predestined to become rapist or child molesters.
No, but all people are sinners, and some are given up to their own selfish desires and passions (Romans 1), and some unfortunately become rapists or child molesters. As for God, though, using Paul's words in Romans 9:22-24, in desiring to show His wrath and to make known his power, He has endured with much patience these vessels of wrath prepared for destruction, in order to make known the riches of His glory for vessels of mercy, which He has prepared beforehand for glory, even us whom He has called, not from the Jews only but also from the Gentiles.
Once you're saved you are predestined to adoption, to be conformed to the image of God, to be justified, to be glorified, to redemption.
The opposite is true. As Paul says in Ephesians 1:4-5, God chose us in Christ before the foundation of the world, that we should be holy and blameless before Him. In love He predestined us for adoption to himself as sons through Jesus Christ, according to the purpose of His will. The saving comes at the point of the Spirit's work in our hearts, which -- as in Acts 13:48 (
"... when the Gentiles heard this, they began rejoicing and glorifying the word of the Lord, and as many as were appointed to eternal life believed...") -- happens for each individual at the time God appoints.
All of these things take place at the Rapture.
There is no "Rapture." Jesus's return is certainly a rapturous event, but there is no time that God takes His people out of the world. He is with us every step of the way -- walking with us even as we walk through the valley of the shadow of death (Psalm 23), and when Jesus returns, it is a once-and-for-all event. The judgment ensues, the ones on the wrong side of that judgment are sent away, and eternity begins. But that's a whole 'nother can of worms, right? :)
Predestination starts at salvation.
Again, As Ephesians 4-5 says, God chose us in Christ
before the foundation of the world, that we should be holy and blameless before Him. So for those who are predestined to eternal life, that predestination occurs
long before salvation is actually effected in any individual's heart. Continuing, in love God predestined us for adoption to Himself as sons through Jesus Christ, according to the purpose of his will.
Grace and peace to all.