You can't be fired simply for belonging to a religion.
However, belonging to a religion doesn't legally excuse your other actions such as harassing others based on their religion/sex/whatever.
So, you can belong to the Church of Satan, and even tell people that you belong to it -- that's your business. But you can't harass Christians for being Christian. That's their business.
Similarly, you can believe there are only two genders and those who transgress those boundaries are wrong. That's your business. But you can't harass coworkers based on those beliefs. That's their business.
If yes, then it would mean that wearing a "there are only 2 genders" tshirt would essentially count as harassing a protected class based on their belonging to that protected class. Which seems like pretty clear grounds for termination, and no "this is just my religion" excuses are going to help here.
Just like wearing a quote from the bible on your tshirt saying that women aren't supposed to hold seniority over men would very certainly get you fired as well, despite that being a part of your religious textbook and you belonging to that protected class.
Dispelling a myth here, the Bible doesn't actually say "women aren't supposed to hold seniority over men". It is true that it has been used in this manner and interpreted by certain organizations as such. Strong lined Complementarianism [0] espouse this belief.
However, the conclusion is not supported by the text and context nor by the rest of the Bible. [1]
To use a verse already quoted here Galatians 3:28. "There is neither Jew nor Greek, slave nor free, male nor female, for you are all one in Christ Jesus". This verse has everything to do with equality and nothing to do with the topic it was used for elsewhere in this thread. ( read it in context and you will see ).
I know I may get flamed/down voted for this but it is extremely important.
[0] https://en.wikipedia.org/wiki/Complementarianism
[1] https://almostheretical.com/episodes/authority-over-a-man
In the macro, it's relevant to issues of school/workplace speech in the sense that it's good to remember that major religions are awfully large tents and represent a wide plurality of beliefs. Christianity is not necessarily synonymous with any particular belief regarding gender, etc. The same could be said of other major world religions.
I'm an atheist and therefore don't have a horse in this race. But it's one reason why merely identifying as belonging to a religion is fine in the workplace, whereas espousing specific religious beliefs that disparage others is a problem.
The comment thread was specifically regarding religion so it is entirely applicable and important.
There are plenty of examples on HN where religious documents other than the Bible or the Pentateuch are discussed. [0][1][2]
Religion and/or the lack thereof impacts our culture and politics in outstanding ways. To ignore them or not discuss them leaves us blind to significant reasonings that have built the world we live in today.
[0] https://www.google.com/search?rlz=1C5GCEM_en&q=site:news.yco...
[1] https://www.google.com/search?q=site%3Anews.ycombinator.com+...
[2] https://www.google.com/search?q=site%3Anews.ycombinator.com+...
Just like wearing a quote from the bible on
your tshirt saying that women aren't supposed
to hold seniority over men would very certainly
get you fired as well, despite that being a
part of your religious textbook and you belonging
to that protected class.
Do you honestly not see a difference between believing a thing, and emblazoning that thing on a t-shirt that your coworkers have to see?