I was tempted to reply to the original question because it implies that there is (only) one correct way to build an operating system, and once you've arrived at

I was tempted to reply to the original question because it implies that there is (only) one correct way to build an operating system, and once you've arrived at the correct answer any duplication of effort is pointless. I find that a quizzical approach. I suspect the downvotes come from the way 'diminish' phrased the question. Linux is implicitly being used as the standard against which FreeBSD is measured, but the question implies ignorance of FreeBSD. Imagine the tone of the responses if the OP has written, "I know linux but not FreeBSD. From a technical perspective, where do they not overlap?"