I just verified some numbers and, not meant to be an insult to whomever produced that dropout drawing, but dude, get your facts straight!
Using a 415mm chainstay length (as spec'd, so c-c BB to dropout) and subtracting for the bottom bracket shell, you have a hypotenuse of roughly 390mm for your triangle. Nudge that chainstay 3mm (120 -> 126) or 2mm (126 ->130) and the angular deflection is 0.44 degrees and 0.29 degrees respectively. While cold setting may be nice for quickly slipping a wheel in and out, to say that not cold setting is going to cause long term harm to the frame is a bit misleading. Old dropouts crack regardless of spreading and I'm guessing most people cold setting frames aren't going to bother trying to adjust out a <0.5 degree angle on the dropout. They likely don't even have the proper tools to measure that angle. Perhaps at 120 -> 130mm you could start seeing some issues but that's a pretty rare thing.
And even if I felt like the angle was an issue, it still wouldn't stop me from spreading the stays on old aluminum Cannondales, because otherwise you couldn't do any updating with those frames
