If you were able to show me that you could hit a six inch plate at 100 yards with open sights I would have no problem calling that ethical... In my experience, most people can't. If you can kudos, seriously! I know I can't...
I think your under estimating your ability,100yrds is not that far.you should try it I think you would be surprized unless you have bad eyes limiting your ability to see the target.scopes can be a hinderence at close range on a deer as all you see is a brown blob in the scope and can tell if your on the front or rear of deer,that why I like raise scope mounts so I can drop down to iron sights and see where I'm aiming.