You begin by saying you disagree, but the rest of your post sounds entirely aligned with Spooner's statement (you should include the quote).
Law defines acceptable behavior, and requires that all lives either be brought into conformity with the law. Any who persistently refuse to comply will ultimately be killed. When law is asymmetrical and assigns some the duty of serving others, the result is slavery. The slave has no direct recognized value and is required to serve as a tool of the political master, and any who are not of sufficient use (refusal to pay taxes or to serve in the military when drafted for example) will be punished until they either serve or die.
The god of the Bible is defined as both truth and love, but most who call themselves Christians seem to focus on the story of atoning sacrifice far more than on the core teachings of love for neighbors. As a result, they are just as ready to demand aggressive coercion through the political system as anyone else is.
RE: The state, slavery, and sin