Sure, but you're missing the point about how laissez-faire families affect the genes that children wind up with.
Identical twin Jane marries a boring guy with a job and they have a
few kids who grow up to be job-holding non-criminal taxpayers.
Her identical twin Joan gets impregnated by various sexy guys who
shortly thereafter get shot, imprisoned, or vanish. Her kids grow up to
be sexy, unstable individuals.
A traditional society encourages more women to marry stable
breadwinner. A 21st Century society encourages women to indulge their
hormones. The smarter ones figure out what's in their best interests,
but the dumber ones don't.
For Sailer's mechanism to impugn the "laissez-faire family," though, we'd need to see a substantial effect of shared family environment on marital status and mate choice. The standard result, however, is that shared genes can account for the greater propensity of e.g. children of divorce to eventually get divorced themselves.
Perhaps, though, Sailer is talking about non-shared environment - which absolutely has to be important, because even identical twins raised under one roof are far from identical. If so, I'm still puzzled. Why single out "the laissez-faire family" for allowing "sexy, unstable" guys to reproduce, when your real complaint is a society-wide decline in traditionalism? If, adjusting for genes, family structure has little effect on how kids turn out, don't changes in family structure look like a symptom of the retreat from traditionalism, rather than a fundamental cause?