*But actually it's not really. In today's world, with varying family types and options for care, it is possible for people to have children and give their all to a company. For many (most?) people that isn't the best option, but it is possible.
From the perspective of the founder - obviously that's a personal choice. I personally wouldn't be looking to start a new venture and actively seek funding if my wife was pregnant, more than likely waiting it out for a few months won't hurt anything. Even if you are in a situation like you described, being pregnant takes up a lot of time that can't be outsourced, like pre-natal doctor visits. Also in both of my wife's pregnancies so far she's had to be rushed to the hospital during the pregnancy and spend a few days there, and on the last one she had to have a fairly intense emergency surgery. Honestly in my anecdotal experience those situations aren't uncommon.
On the other hand if I was already actively working on a startup before the pregnancy and needed to close another round before the baby came, I'd do my best make that happen.
[1]Actually, there's a strong argument that biases based on appearance produce gendered discrimination, but that's another issue.
This is the part that I don't get and that I feel like a lot of comments on this thread are talking past each on. This isn't about just having a family (right?) it's about actively fund-raising while expecting a child. I would not only agree with that last point you made but go so far as so say that I strongly prefer to work for people who have children / families (or at least a respect for the institution of family) as I believe that makes them more empathetic and relate-able. That still doesn't mean it's a great idea to start a startup and raise funds while also expecting a child.
EDIT: FWIW I also don't think that our system should enforce this, whether it's a good idea or not, and yes it's absolutely unfair that it's gendered - or at least it's unfair that an expectant father is more able to hide the fact that he's expecting than a mother. I'm not sure that it's reasonable to expect a VC to ignore that once they know, though.
Thanks to modern contraceptive methods getting pregnant is a choice. The same as doing a time-intense hobby. If you would not finance someone who openly says that he/she will not give up his/her time-intense hobby for the company, isn't this the same as not financing people who are pregnant?