Imagine a group of researchers studied a group of primates and they came to the following conclusions:
Some of the subjects were larger and heavier than others
Some of the subjects seemed intensely interested in defending their territory; others didn't seem to care
Some of the subjects spent significant time caring for the young; others offered minimal support
Some of the subjects attempted to have intercourse with multiple partners; others only maintained one relationship
Some of the subjects were forced out of the group after reaching a certain age; others were allowed to stay
If the researchers just charted behavior there might not be appear to be much rhyme or reason as to why certain behaviors occurred. But if they noted behavior in relation to sex then suddenly those actions become much clearer: Males for the most part have a certain behavior pattern; females have another and understanding that sheds great light on the actions of the individuals.
I read this book because I was writing an article about trans women competing against cis women in sports and this book was recommended to me. It has a large section (30 pages) devoted to this topic and I was interested in reading it and that is the topic that I have a lot of expertise on. Here's one line from the book: " Researchers discuss the scientific evidence that women, on average, perform better in endurance sports than men." (pg 129). Ah - come again? Last I checked the Olympics has many events that test endurance and elite women don't beat men in those competitions (the idea that women 'might' be better at ultra-endurance than man comes from their smaller size and greater stores of bodyfat). He also states: "there has never been a concerted effort to recruit significant numbers of women to try out for the NHL, NFL, PGA, or NBA" He then notes the time Mark Cuban offered a tryout to one of the best female players ever and he follows up with "what if other owners had done likewise at the same time?" (pg 132) as if to imply that if only more women were invited to play on these teams we would be seeing so many more of them on TV - as if the millions of dollars and huge fan base and excessive TV time that athletes receive isn't enough motivation to succeed.
His basic position is: there are some women that are stronger than some men; thus making the claim that men are stronger than women untrue; thus it is sexist to separate sports into male and female categories, it should just be "best player plays". He believes this would cause an increase in female participation and success in sports. I believe the exact opposite would occur.
Humans express sexual dimorphism, it is a basic fact. It isn't sexist to say that as a man I can't bear children, it just true. It isn't sexist to say that on average, or at maximal potential, men are stronger or better at sports than women. Certainly both should be treated equally under the law; but that doesn't mean we are the same. Men and women are not clones that happen to have slightly altered exteriors. I would hope a veterinarian would treat a cat and a dog with the same love and respect and would not show preferential favoritism to one over the other. I would also hope that the Vet would understand that the physiology of those two animals is different and they might require different treatment; so to I would hope that people understand that men and women are not the same and that sex does indeed matter in some instances.
Certainly it is an admirable goal to eradicate either blatant Sexism or unintentional sexism, but in that process we can't forget who we are or where we come from. Sex, and gender, are a fundamental part in almost any animal's life, and they play an important part in understanding who we are and how we behave. To ignore that is to miss a significant piece of the human puzzle.