SYG has so many opponents because they have no idea what it really means. They think it's a license to kill. It's true value is to remove the burden of proof that you could have retreated if you had the opportunity. Said opportunity looking far different to someone the next morning who wasn't there.
The Trial had nothing to do with SYG and yet people are still arguing over SYG. If you can retreat safely, you should; who needs all the grief of shooting someone? Of course if someone is on top of you it's kind of hard to retreat.