Its probably never fully explained in most forums because its a complex topic and would take pages to fully cover, but if you want to learn more read up on the "petrodollar", everything you have asked about has been addressed at various places. If I have time later maybe I can post some good links.
Regardless, each country that uses the dollar we lose, another power gains. Every time the demand for dollars goes down, our debts become that much realer, and some other power elsewhere is able to handle their debts better. And this directly correlates with a nations ability to field an army and fight wars. "Building up an army" after a war has been declared is no longer possible in modern wars; the war would be over well before that. (This is another interesting topic to read up on). And guess what, countries who have a lower cost of wages can field a much larger army than we can on a lower budget. Yes, I realize that bigger doesn't always mean better, but again our technological advantage is also attributed to our high military spending, which is supported by the dollars reserve status. So indirectly, if a country stops using the dollar, our army will be diminished to some extent through decreased spending, while another countries military will be boosted.
Sure losing one country may not bring the entire system down, but when planning your countries existance on the scale of decades or centuries in advance, the elites won't give a shit about morals because our enemies won't either. You don't get to be a superpower for an extended period of time without getting your hands dirty.
Regardless, each country that uses the dollar we lose, another power gains. Every time the demand for dollars goes down, our debts become that much realer, and some other power elsewhere is able to handle their debts better. And this directly correlates with a nations ability to field an army and fight wars. "Building up an army" after a war has been declared is no longer possible in modern wars; the war would be over well before that. (This is another interesting topic to read up on). And guess what, countries who have a lower cost of wages can field a much larger army than we can on a lower budget. Yes, I realize that bigger doesn't always mean better, but again our technological advantage is also attributed to our high military spending, which is supported by the dollars reserve status. So indirectly, if a country stops using the dollar, our army will be diminished to some extent through decreased spending, while another countries military will be boosted.
Sure losing one country may not bring the entire system down, but when planning your countries existance on the scale of decades or centuries in advance, the elites won't give a shit about morals because our enemies won't either. You don't get to be a superpower for an extended period of time without getting your hands dirty.