And Severus would ask what the hell he expected, what with his entire familial worldview being to reproduce, but it's a pointless potential exchange; if Lucius's excuses are poor, Severus's are abysmal. He doesn't even believe in the blood purity war, and his choices were ones made out of furious injury. (Perhaps understandable, in his case, considering the abuse from all other sides, but it's in the past, now.)

"If it's working, then it's fine." His tone suggests that it's not any of his business to approve or not anyway - the Malfoys will do what they think the ought to, and ultimately it isn't his concern.

Nearly charring Lucius's arm off by proxy, however.