Any material can have flaws from the creation process. I have seen some really expensive machined parts be scrapped during the mfg process because cracks were discovered, and that was "billet" 4140 steel from a good maker.
But I still say the average carbon, or steel, or aluminum frame would be designed to take any normal road stress with TWICE the maximum weight rating loaded onto the bike.....too much bad press when a frame fails and the rider is hurt or killed due to the failure. Nobody will ever forget those REI frames failed, or that they tried to slough the responsibility for that off onto the people who make frames for them.
Bill