The VC is projecting here. He has a family, his work requires being on nearly 24/7, and he cannot imagine having kids and his stressful career without his wife taking care of the domestic duties full-time. He's looking to fund entrepreneurs with similar commitments to their work.
The sexist assumptions I think the VC is making here: Married men have a wife like his, taking care of domestic duties so they have more time for work. Married women at this caliber do not have a stay-at-home spouse, they will need to spend more of their time away from work. There may be underlying concern about more children and that potential impact, too.
While biases significantly lower efficiency, it's a deeply rooted part of the human brain. Quick judgements made all the time based on years of interpreting patterns. I do think VC's like this lose out on great talent because of their biases. Unfortunately, the onus is on OP to allay the concerns of investors even in the face of an uncouth line of questioning.
While I liked OP's article and it is commendable to push for change for those who come later, there is also a practicality for the here and now. A greater attempt at diplomacy in the face of prejudice is a more productive way forward. Understanding WHY people are asking what they are asking is often more important than taking statements at face value. Answering their questions by drawing parallels within their own prejudices and biases goes a long way.
I don't think that it is unreasonable to consider any parent as having more important things than startups to do.
"According to the U.S. Census Bureau’s Current Population Survey, in 2014, 47.6 percent of women between age 15 and 44 had never had children"
Sure, because the former is a superset of the latter.
If you meant instead that "childless Women is a (significantly!) larger group than Mothers", even that stat defies meaningful comparison by including teenagers, clear down to 15-year-olds. A more relevant comparison for this workplace discussion would be constrained to a post-college-age group (say, ages 21-44).
This is a hard balancing act, and requires significant time discipline and a very clear understanding of who is doing what when. We're also fortunate that we can afford in-home childcare, and have an absolutely wonderful nanny; most people don't have that luxury, and I'm well aware that it affords us certain options that make hard choices merely difficult.
Having a child is, for an entrepreneur (male or female), a hurdle that does demand action planning and confident communications with potential investors and partners. But I simply don't accept that it should ever be considered an insurmountable obstacle by investors.
Unfortunately, investments are one area where it's hard to say that "the free market will correct this," because it's impossible to quantify the value of companies never funded and products never built.
There's really no question that mothers, and females in general are statistically riskier investments in todays society.
That said, startup investing is a real outlier in respect to regular investing. People specializing in it often are motivated by more than generating larger returns, as a return-oriented investor would surely find other fields to be more lucrative from a risk standpoint.