We've known that in theory your compiler et al can be backdoored but in practice we can feel a lot safer compiling our own software than using proprietary binaries.
I think that might be where we disagree. Without a competent security audit I think you are falling back to trust.
Open Source vs Closed source is not where I or the security professionals I know put most trust emphasis. I would enthusiastically trust something closed from Google over a rando open source project.
But back to the original point, even the most basic audit steps are the same on an open source project vs closed one. Observe what the binary does & inspect it for standard patterns.
But note you are now adding a lot of extra preconditions that are largely not available.
The counter argument is reverse engineering & black box audits are actually easier than getting the conditions right to trust code audits. As a bonus they work regardless of the code availability.
So you can trust your disassembler and strace, but not your compiler? Your method is just vulnerable to another flavor of trusting-trust. What about the compiler that built your rev-eng and blackbox tools?
Trusting trust is one of the seminal talks in software.