I've still not read a single post which explains why this is a bad idea other than narrow minded nationalism.
Maybe it's not a "bad" idea, it's just an incredibly unrealistic one. Why doesn't everyone follow the same laws, is basically what you're asking. At that point, there's no point to distinguishing between countries.
But I am quite glad that I am not subject to the laws of certain other countries on this planet, and that country's inhabitants might feel the same (or agree, and wish they could live somewhere else!).