You seriously need to read up on biology, specifically with regard to the effects of hormones on organisms' bodies. Beyond that, though, the differences in human anatomy among people born with vaginas vary significantly—to such an extent that you transphobes thought a cis woman athlete was trans.
In basketball, for instance, a 6'6" cis woman has significantly greater an advantage over a 5'10" cis woman than a trans woman has over either of them. Additionally, I'm a pretty well-built cis man and any female athlete could absolutely kick my ass at their given sport—at any point in my life.
I'm naturally strong and large and I put on muscle easily, but even if I spent the next 5 years training in, for instance, tennis, Venus Williams would wipe the fucking floor with me from one end of the court to another. The idea that my dick gives me some sort of stat boost is absurd.
Trans women want to compete against other women because they are women, and their physical capabilities place them well within the range of cis women's athletic capability ranges. Which is why they very rarely win against other women athletes!
Forcing trans women to compete against cis men endangers them, because of transphobes like you who embolden the bigots who attack and murder trans people simply for being trans, and places them in situations with the cis men who in general assault both cis and trans women at alarming rates.
But again, I urge you to remember that trans MEN also exist, and compete against cis men, and piss in men's bathrooms, and they don't do this to try to sexually assault cis men—they do this just to live their fucking lives.
Meanwhile, given the statistics, you are in effectively zero danger of ever ever ever getting sexually assaulted by a trans woman. It happens so incredibly rarely that you're more likely to win the lottery. Banning them from sports and bathrooms achieves literally nothing, buys you no more safety.
But what the fuck do you think happens when you take a trans woman and force her to be in the locker room and the bathroom with cis men? Y'know, cis men? Heard of 'em? Biggest sexual predators in our species? Statistically biggest sexual assailants of both cis women and trans women?
So in order to buy yourself and other cis women statistically zero more safety, you're throwing trans women to the wolves where they'll undoubtedly be raped by cis men. You gain nothing, and you spend their lives for it. This is sociopathic. It is cruel and it is wrong. You are wrong.
Meanwhile it is so extraordinarily easy for cis men to rape women and get away with it in this miserable country. Why on EARTH would someone go through all the stigma and trauma of being trans just to achieve that? Nobody's doing that! Nobody is trans to sexually assault women! It's absurd!
In a country where rapists go free because judges say shit like "think of this boy's promising swimming career" do you really think there's any motivation or need at all for someone to be trans in order to commit sexual assault? Especially when that invites even more scrutiny and wariness.