The lower a level, the easier to add a backdoor, the harder to audit. To add the backdoor to the handwritten assembly code is much easier than to do this with (reasonably clean style) C, and both are easier than add it to Standard ML or Haskell code. The same is true with verified formal hardware description specifications, Verilog and lithographic mask.

So the path toward trustworthy computing, besides cheap fabs, is higher level tools, projects like Kami and CakeML, proof checking, automatic verification and synthesis.