stupid question

Ok. I know this is a stupid question, and that there is no real answer, but I have to ask it anyway. Why is it ok for this country to threaten use of nuclear (or other) force to demand compliance of any other country not to develop its own nuclear arms program, i.e. to protect itself?

Granted, I don't believe that anybody should be killing anyone, and much less on a wide scale whose ecological ramifications are innumerable, irreversible and eternal. But wasn't there something somewhere written about leading by example? What right does the U.S. have to "punish" the rest of the world? (and here I am not limiting myself to questions of nuclear contamination but also of our massive overconsumption of petrochemicals). And why shouldn't others be allowed to protect themselves against imminent danger (Halliburton trucks just waiting to rumble across the desert).

God knows it is far more complex than my simple mind can grasp, but shouldn't we, every so often, try to look at things simply? For a regime who claims moral authority... they might want to brush up on the Bible, for starters (Thou shalt not covet thy neighbor's... oil).