You don’t believe in executing someone just for stealing when you can have the person work off the debt from the theft, or pay a fine for it, right? Some sins are more serious, because I can’t undo murder, or can’t undo a person’s incurable STD from raping the person.
The matter of whether or not I belong in heaven or hell is very different from the punishment for the crime. Let God sort who belongs where out.
When I hear someone decide that a certain sin/crime should be punished more severely because someone decides that adultery (from an earlier post in this thread) is a capital offense because they have their own personal issues and want to extend their interpretation of what they think God's Will should be as "justification".