"nor does it necessarily follow that you have to have explicit warrant in the NT for everything you do"
Where not talking about what type of shoes you wear on Sunday - we ar talking about taking an human life in the name of Jesus Christ. This has turned out to be such a black spot on the history of the RCC, how could you possibly see it as a good thing?
"the death penalty for heresy was certainly not contrary to the Spirit under the Old Covenant."
Different covenant, different rules. Israel was an earthly kingdom and engaged in earthly warfare.
"My Kingdom IS NOT OF THIS WORLD. If my kingdom were of this world, then would my servants fight".
Old Covenant was not revoked, however...
And it is a black spot on the history of CHRISTIANITY. Protestants burned people same as Catholics. You can't single out the RCC on this--Prots are as guilty as the RCC.