Foreigners often have difficulty with this because rules in most western cultures are negotiable. You can appeal to common sense. You can argue your position and modify your environment. This is generally not possible in Japan. The idea of drawing a line, as you have described, will almost certain end in an extremely difficult position if you wish to be inside.
I think there are 2 happy places in Japan. You can decide that you aren't going to follow the rules and accept to be outside. Everyone will smile and be polite. They will be very helpful to you. They will praise you on being able to use chopsticks, etc, etc. You will forever be an honoured guest.
But not many people want to be treated as a guest in their own home, so most people want to be inside. This is also fine, but you have to learn the crazy rules and follow them exactly. You have to be OK with being reprimanded for making the slightest error. You have to slot yourself into society exactly where they put you. You have to do what is expected of you.
Where you get into trouble is when you want to be inside, but you want to pick and choose which rules that you wish to follow. Or if you wish to negotiate those rules. Or if you wish to convince others to play by other rules. That's just not going to work in Japan and I think it's why most foreigners don't stay, even though it is technically very, very easy to immigrate here. Like I said, especially if you have a very strong moral sense of right and wrong, it's going to be really, really difficult unless it happens to match exactly the sense of right and wrong in Japan (which is pretty unlikely if you were not raised in Japan).