I mean, imagine if humans had a mating season. Don't you think most non-essential businesses would close down? Nobody's mind would be on work; it'd probably be an ancient and ingrained habit that we all ignore everything but food, shelter, childcare and mating during (say) a month in the spring. And as we developed culture and civilization, we might enshrine a long holiday around that time. And the college kids would agitate on behalf of the oppressed working poor, who had to take jobs during the mating season and were thus deprived of their own best chances to reproduce. And the entrenched upper classes would sniff that there were plenty of other hours in the day for mating, even if one did have to work for six or eight of them.
The sense I get right now is that "You got yourself pregnant. Many of our other workers, male and female both, have avoided this. Now, while we are willing to bend a certain amount to accomodate you, because we like the idea of a new generation paying into Social Security and we're not total bastards, the norm is non-pregnancy and our rules go to upholding the norm. You're a special case and we can't go around making exceptions for special cases."
A disclaimer: the people I personally work with have actually been great, and I think if I'd asked my boss for some under-the-table considerations - like if I'd had truly wretched morning sickness or something - I might have been able to get them. I mean the official rules, which put a week of contagious stomach trouble from the flu in with two months of non-contagious stomach trouble from the baby. And a lot of people get bristly if it's suggested that these two things should be treated differently - that pregnant people deserve some sort of "special" treatment, because it's not fair. You feel sick, you use sick leave. Period. Heck, I admit a certain sympathy with that position myself. It's certainly easier.
I just have been wondering if our definitions of "fair" and "normal" and "special" would be different if men, or men and women both, could get pregnant.