And if a man is something with a penis, then imagine that a man removes all of his genitals in surgery, why will he still remain a man after surgery?

A man isn't merely "something with a penis". I realize that QT tends to phrase GC arguments as simplistic, in order to convince you that they are the only purveyors of nuance, but there are many signs of maleness that are not a penis and/or testicles. Delete the penis/testicles and there are still bushy eyebrows, sloped forehead, adam's apple, facial hair, broad shoulders, large hands/feet, tall stature, etc. Surgically alter all of those, and there is still, at the end of it, a set of XY chromosomes easily checked by a blood test. Those will never change absent intense genetic modification. And even if those were to change, many males have obvious behaviors and mannerisms that originate in the way they were raised and the years spent being perceived as male and stewing in the chemicals a male body creates.

A male can appear feminine, and this may help him cope with life, but he cannot become female. We can revisit this when it's possible to change chromosomes, as it will become a more nuanced question, but right now it's far too easy to tell. It's so easy to tell that 23andMe now gives you results based on your self-reported sex so that dysphoric trans women don't have to be confronted with an XY.

https://customercare.23andme.com/hc/en-us/articles/115015843628-I-m-Transgender-Will-This-Impact-My-DNA-Test-Kit-Experience-