There would be nothing stopping an SLR aficionado from likewise pronouncing that he takes more human photos with an SLR. I'm sure such a person can be found.
You need look no further. I am he.
To me, a rangefinder forces me to be
much more clinical than an SLR. If I'm not, my pictures will be out of focus and improperly framed. Why? Consider the following:
I. Focus
An SLR's entire view changes as you focus. While extra focal aids are in the center, you can look at any part of the image to help you focus and if you're out of focus, you know it because the view is blurry.
A rangefinder's focus is all in a patch at the center and the overall view is crisp all the the time. The split image works best with objects with clear edges that aren't necessarily available. I have not only ended up with shots completely blurry because I forgot to focus at all since everything looked crisp, there are shots I've just had to give up on because there was nothing I could use to get a clear split image off of.
II. Framing
An SLR gives a through-the-lens view that's generally 90-100% of the actual image area. Most aren't 100%, but the loss around the edges is small and more importantly, absolutely consistent from shot to shot.
A rangefinder has framelines that not only can go invisible in the wrong light, they move in your viewfinder as you focus. Oh and the beautiful thing? The movement is a
feature because of the need for parallax correction. Yet another thing I must pay careful mind to that's bleeding attention away from like... composing my shots.
No, I don't secretly hate rangefinders and the problems above can fairly be largely ascribed to the fact I'm more experienced with SLRs than RFs, but even as experience makes these issues less of a problem, they don't become any less true.
SLRs are generally a much smoother experience for me than RFs. However, I do not extrapolate from that that because I've taken much more dramatic and beautiful pictures with my SLRs, that SLRs are inherently more dramatic and beautiful. That's just as ridiculous as claiming that rangefinders are more human.
Different tools shape how the wielders use them, but that shaping is not consistent between different wielders.