"And if that post op person with a penis is attracted to women, you would still insist they use the women's toilets?"
What is the purpose of asking this, I wonder? Is this trying to pretend that a transman with a surgical simulacrum of a penis is as much a rape threat as a man? Because if that were really the concern, then a lesbian with a strap-on would be as much of a threat (unless you believe that testosterone or identifying as a man do of themselves make you more likely to be a rapist.).
Although this seems to make the same ole mistake of assuming that the key issue is the actual threat posed by the individual, rather than the perceived threat. So, a non-passing transwoman could be objected to in women-only spaces both on the grounds that they are obviously not female (and we think such spaces should be segregated on the grounds of sex not gender), and on the grounds that allowing obviously male people into the ladies allows non-trans predatory males a free pass. The first is specific to the person involved, the second is general.
"...people should use toilets based on the genitalia they had at birth." That is a pretty weird definition of sex there! Actual sex isn't totally determined by the appearance of the genitalia at birth (as many intersex people know, especially those who suffered unwanted genital surgery as children), just that for most people, the appearance of the genitalia at birth is a reasonable estimator of sex. Of course, the definition has been attempted this way so it can be claimed that changing the appearance of the exterior genitalia and secondary sexual characteristics is changing sex, when it is just cosmetic surgery.
What would an answer that shows respect and consideration for females be? Not pushing your way into the ladies when you are male. If safety in the gents is the issue (which could be because you're a non-passing transwoman, or just a drag queen, or a small-bodied transman, or a transman who needs to change their tampon etc), then until we solve the problem of male violence, a sex-neutral separate cubicle would work.
So, putting tampon bins in the gents would not make transmen safer, since as all us ladies know, you can hear the bins opening! Using the private cubicle, could just be (as some of my gay male friends are) that you are shy of peeing at urinals, or a male who sits to pee for religious or cultural reasons, or just anyone who prefers a little more privacy.
Which seems to me to be a solution that increases general safety at minimal cost, whereas letting all of female sex PLUS those with a female 'gender identity' in obviously decreases it (since it itself destroys the very safety that transwomen claim they are seeking in the ladies!).
Letting anyone who identifies as X enter the preferred loo, that is surely the only suggestion that decreases safety for all concerned --apart from gender-conforming, straight men who would be as safe as they always were! So why would anyone prefer that if safety of us all was actually what mattered?