The difference is that all of the other scenarios you mentioned don't work by default under standard execution privileges, and/or require additional setup beyon

The difference is that all of the other scenarios you mentioned don't work by default under standard execution privileges, and/or require additional setup beyond just executing the program. /proc/$pid/mem just works with any program under Linux. That's a pretty fundamental difference. Like I said, if it weren't the default behavior on Linux, I wouldn't care. But as it is I don't think you can meaningfully say the default Linux environment is "not a reasonable environment" for running secure software while I am happy to say this about, say, running with root privileges, or having a debugger inserted, or loading non-default kernel modules. The idea that unsafe is supposed to only cover "deliberate" invocations is kind of silly, IMO. That is not what unsafe means. A function called "get_unchecked_index_this_requires_a_bounds_check_be_careful" still needs to be marked unsafe. But even if somehow this distinction could be made meaningful, this turns an accidental bug that lets you manipulate the file path into full blown arbitrary code execution.