I can't make my mind up about this, but actually, I think I'm more on the side of he is being reasonable.
There must be women out there that have been turned down for a job because the interviewer had second guessed and decided they probably will want children, when in reality, they don't. Or don't have any immediate plans to at least.
I think it can be very unfair on employers when women take a job and then become pregnant shortly afterwards, only to return to work for a couple of months and get pregnant again.
But of course, women shouldn't be prevented from employment just because they want children at some point.
It's a tough one, and I don't think there is ever going to be a situation that is fair to both employer and employee.
Maybe smaller companies that would genuinely struggle with maternity leave should be able to ask, but larger companies that could easily swallow the extra costs should still be barred from knowing.