I base it purely on my experience (in real life) where I have never had a single problem with tyres magically exploding or debeading running 215/45 on 9J. I can pretty safely say that I have gone through more tyres in the last two years than most people on here.I have even broken a wheel running a 215/40 on a 9J and the tyre did not deflate. I smashed a 215/45 on a 9J into a gutter destroying the wheel and again the tyre did not deflate or debead. The only time I have had a problem with leaking was when I pinched the bead because I suck at fitting tyres. Actually now that I think about it, the rear wheel/tyre setup on the picture in my avatar is 215/45 on 9.5J, again, no problems.
One thing that I do understand people getting upset about, is beading the tyre.
Often people will exceed the recommended beading pressure either using an chemical explosion or a very high pressure air tank.
If you use a bicycle tube while beading the tyre it is possible to bead the tyre using around 50psi if the stretch is not too crazy.
One other way if you are going for crazy stretch is to stretch the tyre on a less-wide wheel to pre-stretch it so you can put it on your really wide wheel later.
Also the wheels you are using make a huge difference. The best wheels I have seen for stretching tyres are Work VS-KF, they bead so easily.
So basically, I have nothing more to go on than the evidence of what I have seen and experienced in real life. Which I realise can be confusing for many people on internet.
edit: I do of course realise that as someone who has been known to partake of the occasional drift, my credibility is through the floor as far as SAU goes