Until you show me full size versions of those images you shared, which appear to be quite sharp to me, that prove they are soft and needed IS (vs. say better focus), I'm sorry but I have to disagree tat it is "completely, patently, and demonstrably ridiculous." I've shot enough with a 50/1.4 to know that my shutter speed is most often well above the 1/focalLength and even above the 1/focalLength*2 baselines to produce shake-free shots except in more extreme circumstances (such as your second photo, however that would usually be where you jack up the ISO to compensate.)
If we were talking about an 85mm f/4 or even f/2.8 lens, I would completely agree with you...but 85mm lenses are f/1.8 or faster, 50mm lenses are usually f/1.4, and most frequently used at their faster apertures. Additionally, with wider fields, it takes more camera movement to result in meaningful motion of image detail at the pixel level, so blur from camera shake becomes less and less likely the shorter the lens.
And what's with the hostility? Wrong side of the bed day today or something?
First off, no hostility at all, just a very strong disagreement with your untenable point of view. Calling something sh!t that is sh!t is not hostile. I'm just doing an Arthur Morris on you.
Second, you are now putting limits on aperture and iso for focal lengths, you can't do that. What if I want/need f8 and 1/4 at iso 400? Then IS would be good to have. Just because a prime lens might be between f1.2 and f2.8 doesn't mean that aperture is appropriate for the image to be taken, as per my second image example. Same with iso, I used 800 for the second image and ETTR'd because I didn't want to lose DR between the candle flame and the very dark wall detail, if I'd had IS I could have got more DR, and shadow detail, by going to 100iso.
Third, the size of the pixel and the arc of blur are completely unrelated, assuming you have enough resolution to resolve the arc of blur, as my two images with 2003 sized pixels clearly do, having more resolution would not make the blur better or worse, only reproduction size would. Same as diffraction limits and airy discs, more resolution is not worse, but it doesn't increase or decrease the diffraction.
Fourth, do you honestly think I would post an illustrative example that doesn't illustrate my point? I have posted hundreds of them!
Anyway, here are the 100% crops with zero sharpening or noise reduction on the best point of focus. They are both focused within this 700 x 700px square, the sharpness falls off as you go further away. They both show camera movement as can be evidenced by the shadow/ghost around the front of the monks face in image one, and the fact that the second image crop is the sharpest section of the frame, the point of focus and I were completely static (I was braced against a wall) and my camera is set to not take a picture without achieving focus.