Honest question, the general physical differences between the sexes or even races are undeniable, so why is it so taboo to talk about the differences that almost certainly exist in our minds?
1. Look at https://news.ycombinator.com/item?id=17949340 for a more detailed account of what happened. This specific story is not a case of taboo, it's a case of attempting to publish something that's not science in a science journal, being of course rejected, and reframing the rejection as a taboo.
2. It can be discussed, but this kind of discussion invariably attracts people who are not there to discuss, but only to impose their political/social views. Some because they feel that it's a good opportunity to attack women, some because they feel that the conversation is going to end up being an attack on women regardless. In either case, it's pretty much guaranteed to degenerate into anything but a meaningful conversation.
3. Also, it took us millennia to accept that maybe women are just human beings, after all, and some people still can't accept that, so maybe our society just isn't mature enough yet to have that conversation.
Maybe once humanity has finally mastered the fine art of polite, meaningful conversations on Twitter and Facebook, things will be better :)
edit Reworded a bit.