1) Because female and male are literally defined by the development of those reproductive systems (whether they are functional or not or whether they are removed or altered or not).

2) See above

3) It possible male pregnancy may happen at some point, but it’s a bad idea and a poor use of resources. I feel the same way uterus implants in females for pregnancy too because it’s just so risky and so many safer options already exist. Trying to do that in a male will be even harder because there is less of what is needed already there. My husband and I can’t give birth, but are going to adopt. People should just do that rather than put themselves and a child at risk. Even surrogacy would be a much better choice, although there can be ethical concerns about that.

4) Maybe, although the person would have to take anti-rejection drugs for that to work and they might die (everyone who has tried it so far has). It’s possible genetic engineering could enable it, but I don’t feel like it should be a priority considering the state a women’s healthcare and all the diseases we don’t have cures for yet.

5) I feel like the only way you could really change sex is if you could rewrite your genetic code somehow. If that happened, maybe it would really be a sex change. It wouldn’t change your experience though which would not be typical for someone of that sex so many GC concerns might still apply.