Wow, what a thread. I just happened to trip over the OP's bitch session on another site (while looking for other unrelated info) and out of curiosity came back here to see what all of the brouhaha was about and found it. Just wow.
I'm not going to comment on any of the interpersonal stuff. Its not about me, I have a fairly thick skin, and if someone takes a rhetorical swing at me, I'm fine with swinging back but don't need to take up anyone else's fight.
As to leveling. Yes, I do get that the errors down range from small leveling errors may well be inconsequential. I don't care, I level to the gun anyway. I was an aero engineer, USAF pilot, and later a program manager in very high tech. To me, things are either completely and utterly right or they are wrong. Yeah, I'm kind of binary that way.
I do have a set of Ariska leveling tools which provide similar function to the Spuhr leveling groove and wedges and work well. Just need enough room between the turret flat and the rail to get them in there. And yes, pretty much any very flat and square device will do....like feeler gauges, playing cards, whatever.
So why do I choose to level my scopes to the gun? That is, why is it "right" for me at this point in time.
Well, because I don't shoot off hand very much at all. Bench or prone at very soon to be 68 y.o. I know if I level to the gun, I at least have one datum plane I can count on.
Someone in the thread mentioned shouldering the gun (un-rested and off hand, I presume) and rotate the scope to gravity level with the gun in your shoulder pocket. Grand idea and this fella must be pretty beefy. I have a 6.5 CM in a J Allen chassis and no way can I hold that gun to my shoulder with one arm.
I suppose you really don't need to take all of the weight and can rest the gun on a single point as long as the gun has freedom to rotate around the longitudinal axis and into your natural shoulder pocket.
I shot tournament skeet for many decades and EVERY one of my shotguns has adjustable butt pads to move the whole gun up a bit but also to cant the pad so that it fits into my natural in my shoulder pocket with the gun level to gravity. And everybody, even the guy with the flattest pecs, has a shoulder pocket that is off from vertical. Me, I'm a big breasted boy! haha
With the shotguns and moving clay targets, it really is beneficial to have your and face/eyes/gun level to gravity when the pad is in your shoulder pocket...for a number of reasons.
I now see that there are some chassis and the like with pads that will adjust for cant, but it doesn't seem like very many so I suppose that supports the position of level to gravity with gun canted in your shoulder pocket....if you shoot off hand. Makes perfect sense.
But I would still prefer a scope leveled to the gun with an adjustable pad to take care of shoulder pocket angle issues. From so many years swinging a shotgun, I have come to appreciate just how attune to off angles the human eyes and brain can be. So, I do tend right now to like my guns to be level to gravity. Just feels right to me.
And again, wow...what a thread.