Well, yes, having children is a choice that most of us here were lucky enough to be able to make (good grief, awkward grammar!), but if we all stopped having children humankind would kind of be up shit's creek, wouldn't it? 
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Not likely to happen of course, but if we want people younger than ourselves to be available then somebody has to have kids. And kids tend to interrupt life a tad - at least that is my experience so people who opt to have children need that to be taken in to consideration.
Yes, cancer is very rarely a choice... 
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My work is in principle a very small company, 5 co-ownsers, me included. There are still places like mine where the partnership agreement only allows for Statutory Maternity Leave (6 weeks). We've always been v family friendly (which tbh was one of the attractions when I joined before I had children), and still, I feel a bit guilty that I had 4 sets of 6 monthly mat leave in 7 years. Stupid, really, but I cannot help it and now that I am out of the worst of baby fog, I really feel I owe my colleagues. The funny thing is though, we've all had extended leave for various reasons, mainly mat leave and sick leave (some of it rather extended - see above).
DH never had to consider all that of course... otoh, I know, that he would have loved to have more time at home when the kids where tiny (well, not with screaming DS1 maybe... ).
A set amount of parental leave that the parents can split between them as they wish, seems sensible to me.