Here's the real paradox: the only true freedom to be found is slavery to Jesus Christ. So in some ways, your statement about us being "slaves" to God is correct. We were created to glorify God. That is our purpose. Yet He gave us the choice not to do so... because us choosing to glorify Him when we have the option to not do so is even more glorifying than if we were simply created robots to worship Him.
Only subservience to Christ brings us true freedom from the sin that binds us. And God didn't create a few humans destined to commit sins. Oh, no. By giving us free will, He guaranteed that we would sin. And given that we have no way to measure up, we can either continue in that sin, or turn to the one thing that can save us, the source of our very lives, which would be Him. God can redeem the vilest sinner. Hitler himself could have been saved had he repented and turned to God. That doesn't mean that he wouldn't be held accountable for his actions on this Earth, but he would have avoided the hell that he (and all of the rest of us) richly deserved.
