@steelman @ebel Please don't derail, there's plenty of resources on this question out there.
However, being cis myself, I'll take some time to explain:
It matters for example people with non-binary gender. Society tells them there's no place for them, in this case in a very physical way. Also they might get bad looks or worse due to people's cissexist views of gender which clashes with some people's gender presentation. Some have even been attacked.

@NerdResa @ebel Indeed, I didn't take the non-binary case into account. I didn't mean to offend anyone. This was an honest question. I'll try to find something to read, to learn why would anyone mind someone entering a toilet of their choice. Thank you.

@steelman @ebel @NerdResa in addition to nonbinary people, it can matter for (some) trans women and trans men as well (transfeminine people tend to get the worst of it), and for anyone who just doesn't look the way society expects a woman or a man to look.

If you have to fear stares, comments and physical violence in the toilet that corresponds to your gender, it's good to have a different option. If that could happen in both gendered toilets, even more so.

@steelman @NerdResa I think it very much does matter to enough people. Nonbinary ppl or trans people can get harassed over toilet usage. *You* might not care (good on you! 🙂), but some other cis people do care.

@steelman @NerdResa There are other cases where someone might need to go into the toilet with someone of a different gender: a parent with a small child, someone assisting someone who is elderly or disabled.

@ebel @NerdResa Yes. That is why I asked. I go to a swimming pool where parents of both sexes come into men's locker room with children of both sexes (of course not mothers with daughters) and nobody's got any problem with that. And, believe me, neither my country nor even my city is as progressive as I wish.