This post and the two from christianstudies.wordpress.com are for reference. I’m not commenting at this time.
I will point out that Paul was raised in strict Jewish heritage. He referred to himself as among the best. http://biblehub.com/philippians/3-5.htm It is unreasonable to assume that any of Paul’s references and statements can be taken apart from a context of Hebrew law and history.
It is important to read exactly and not read in.
It is a large statement, not to be abbreviated. http://biblehub.com/text/1_corinthians/6-9.htm
Warning Against False Teachers
3As I urged you when I was going to Macedonia, remain at Ephesus so that you may charge certain persons not to teach any different doctrine, 4nor to devote themselves to myths and endless genealogies, which promote speculations rather than the stewardshipafrom God that is by faith. 5The aim of our charge is love that issues from a pure heart and a good conscience and a sincere faith. 6Certain persons, by swerving from these, have wandered away into vain discussion, 7desiring to be teachers of the law, without understanding either what they are saying or the things about which they make confident assertions.
8Now we know that the law is good, if one uses it lawfully, 9understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for those who strike their fathers and mothers, for murderers, 10the sexually immoral, men who practice homosexuality, enslavers,b liars, perjurers, and whatever else is contrary to soundc doctrine, 11in accordance with the gospel of the glory of the blessed God with which I have been entrusted.
Context is important.
I will also add that I do not condone any sort of extreme punishment, much less death, for sinners.
I cannot support capital punishment in our modern context, but I assent to it in the general sense. I can only justify capital punishment for aggravated murder, and only when egregious, and for violent rape.