Like the organised crime syndicates it draws its influence from, SPECTRE operates via a very strict code. There is the intolerance of failure, and that whole confusing outside observers by pretending different people are in charge every week tactic, but they exist as part of a wider philosophy towards international naughtiness. To maintain their below-the-radar existence, which allows them to effectively manipulate world powers and continue to make loads of filthy lucre without being brought down by a concerted effort by MI6 in collaboration with Bond's pals in America and Japan, they live by a strict doe of loyalty and silence, and the hard retributions that followed violations. That's more stuff pinched from the real-world Yakuza and Mafia, and has been in there since their debut in Thunderball (with the books) and Dr No (in the films). They also have a somewhat moral code wherein they always keep their word, as evidenced from the fate of SPECTRE Number 12 of the Unione Corse in Thunderball. Pierre Borraud was supposed to kidnap a girl for ransom, and ended up having sex with her. As a punishment, Blofeld electrocuted Borraud and returned half of the ransom money to the girl's father as compensation. It's important that SPECTRE is shown to be an honourable bunch, even if they're technically doing dishonourable things.