I`m going to guess that you`ve had more than one confrontation with your parents about this.
Pick your battles. Seriously, I think that is the best advice that could be given. I don`t know enough about you, your parents, or the direct reasons for this confrontation...
But if you know it upsets them, why keep up the behavior. Pack the stuff up, put it quietly out of their view, and don`t talk about it when they`re around. You can still keep your interest without flaunting it in their faces and triggering these problems. If you persist in doing things that cause confrontations, well, you only have yourself to blame.
Clearly you know what pushes their buttons. You don`t have to agree with them - just don`t push those buttons.
And now on to my own personal assumptions and opinions on your situation
It really does sound like you have an unhealthy obsession and some very unrealistic expectations. Japan is no utopian wonderland. There are TONS of countries out there in much much worse shape than the US. Saying the US sucks and is the worst is pretty narrow minded - and doubly so if you`ve never lived abroad and are comparing it to a country you`ve never even been to. Even though I prefer Japan to the US, I would STILL be pretty irritated by your attitude if you were my kid.
Get your priorities straight. Right now, you live with your parents, in THEIR house, most likely on THEIR money. The least you can do is abide by their rules and wishes while you live there. If your dad wants you to be a Christian while under his roof, and throws a fit if you talk about other religions - just don`t talk about it. Just go along with it - if you don`t believe, then going to church or doing whatever else they expect of you shouldn`t matter.
Pick your battles. *sigh*