Hi, guys —
Proponents (or those in favor) of the Death Penalty always use Matthew 18:6 to justify their view, seeing that even Jesus allowed the killing of criminals.
I'm not quite sure Matthew 18:6 was the verse you meant to reference.
Nevertheless, this is a common question; it's even in our searchable knowledge base. There are a lot of quick answers to similar questions that should answer your question, so give it a try.
I searched the knowledge base for you and found these web postings that should help:
I hope this helps,