Re: Adultery
Even though adultery is an act commited between 2 people who consent to the crime, it is a crime against society, rather than a victimless crime as you imply.
Adultery undermines the sanctity of marriage, it cheapens the value of marriage, and that makes execution a suitable outcome, should the crime be proven.
For a society to protect the value of marriage, it must be willing to eliminate those who undermine it.