Poppycock. Where does it say that removing sin from existence means free will has to be removed from mankind? If god is omnipotent he must know a way to accomplish this. Since he's not doing this he's making things unnecessary complicated, it's stupid and useless. He puts his son through suffering, for what? Putting any lifeform through suffering is immoral. He could have done it the moral way, but he didn't. Why?
Also, god has free will, right? Is god a sinner? No. Hence free will without sin is possible. What's his problem?
Why are you following a god that prefers to put sin/pain/suffering upon others, instead of ending it all by simply removing sin from that darn universe?