We can blame von Neumann (et al) and his infernal architecture, where memory stores both instructions and data.

You can blame whoever invented the word "if", as soon as you can branch based on data you can just write an interpreter that turns data into instructions, no matter the architecture.

Not really, most of these configuration as code systems are not executed directly on the CPU but rather interpreted in which case a separate data-only memory would not stop anyone.

von Neumann did not invent the von Neumann architecture. Not even a little bit.

If you want to reason that the hardware is at fault, you should be blaming the Eckert-Mauchley architecture.