In case you didn't notice, they weren't the only ones in that situation. The other guy chose to look for other means rather than murdering a couple of innocent people. Moreover, going by the logic of using the protagonist, only one of them would having been able to survive anyway. The reason I personally hate them is because they weren't bothered with killing other innocent people to get what they wanted, like that chief, for instance. They only ever cared for each other, and treated every other character as disposable trash. There is absolutely no appeal in their personalities or behaviour - the only thing they have going for them is that they were a supposedly good-looking possibly gay couple. For me, that's not enough reason to let them live and keep fucking things up. I'm just pointing out what I think of them, though. You're entirely entitled to your opinion.
Man am I the only one who wants the antagonist couple to live??? Like I mean yeah they were fucked up but that's just natural. I mean, would you let your (only) chance to survive slip out of your hand? They're not evil, just striving for a chance to survive. And it would be peachy and all if you give them a second chance, Author-san.
Also I want more of the inspector (Masakazu, was it?) and Kazufusa moments (づ ̄ ³ ̄)づ kinda shipped them here