I am not sure what statement you are responding to. I am certainly not arguing that. I disagree with your claim that "it is practically impossible find a program without UB".
A study found that, for a particular subset of UB (code that had legal, detectable behavior changes at differing optimization levels), 40% of Debian Wheezy packages exhibited this UB.
I know, but this still leaves 60% of programs without such UB which is far from "it is practically impossible find a program without UB". Also this this was a study from 2013 and many of those bugs found were fixed. Also GCC got UBSan in 2013 (so after this study).
That's "UB that was detected in this study". Since gcc will silently break code when it detects UB and you can't tell until you hit that specific case, the 40% is a lower bound. In practice it could be anything up to the full 100%.
Uhh... mathematics and logic? Since there's no perfect UB detector, one that detects UB in 40% of programs can only be presenting a lower bound. And I don't know why you think C programs rely on UB, they have it present without the programmer knowing about it.
https://people.csail.mit.edu/nickolai/papers/wang-stack.pdf
I submit that that's a small fraction of UB, that much of it would exist at any optimization level.