For 2000 years, the Church has been OK with the death penalty.   Aquinas and Augustine both  were OK with the death penalty.   

Exodus 22:18  "Wrongdoers you shall not suffer to live."

 The argument that evildoers should be allowed to live in the hope that they might be redeemed was rejected by Aquinas as frivolous. If they would not repent in the face of death, it was unreasonable to assume they would ever repent. "How many people are we to allow to be murdered while waiting for the repentance of the wrongdoer?", he asked, rhetorically. Using the death penalty for revenge, or retribution is a violation of natural moral law.

It was only V2 that the church said it was wrong.

I know how I feel about it.