I was disagreeing with that on the basis that only looking at your bottom line when trying to decide what is "economically rational" is short-termist and self-defeating, because everyone benefits from living in a society where women have the opportunity to be as productive as men- and that includes employers who don't have to look at the gender of candidates to make a decision.
The benefits may be harder to measure, but that's why rationality is required, rather than rationalisation of unjustifiable bias ("women have lower expected work output").
The genuinely rational thing to do is to try and ensure that both women and men are equally productive, as workers.
If you want law firms to make their hiring decisions differently, then you have to change the incentives and rules that apply to them, not make false claims that they're being irrational.
Being a churn-and-burn testosterone fest is starting to look like it might have some negative long term consequences.
The OP was arguing that women have a lower expected work output over their career at a company, which is why "economically rational" was used.
So the employers would technically be better off hiring a male over a female with the same skills.