But the pragmatic approach is to assume that data may become executable due to vulnerabilities and design around that fact. Assuming that you can control everything is fanciful and dangerous. Assuming that you control nothing, and everything can and will break is a much safer approach.
The pragmatic approach is to use a toolchain which prevents data being executable. Most high level languages without pointers and direct memory access (excluding dynamic languages) perform this feat quite well.
I disclaim the use of hacks like non executable segments here in certain CPU architectures (x86 LDT/GDT controlled access bits) as they are an afterthought.
So you just have to force every piece of code on your computer to use that tool chain. "Dear Mr Zuckerberg, please make Facebook available in a form that allows me access without needing to rely on dynamic languages and uses a strictly defined toolchain (of my choosing)". Good luck with that.
