"Is it really such a grave sin, if a nation does not want to disappear? Does it have the right to protect itself?"

Protect itself from what? And what do you mean by a nation disappearing? Obviously the real estate is going nowhere so that leaves what exactly? Some vague sense of national identity? Based on what criteria? Skin color, religion, language? What? And who gets to decide? You seem to forget that the White Anglo-Saxon Protestants who once ran this country were afraid "their country" would be sullied by mixing in "dirty Irish Catholic blood" into the gene pool, never mind Italian, Polish, or African. So we've been down this road before. Many of us learned the lessons of history - namely that this nation's greatest strength is its cultural and religious diversity. It's deeply disconcerting to find that there are still those who obviously haven't.