The guy who replied to you is correct, as everyone who paid attention in Econ 101 is aware: there is no reason for the US Federal Government to default, ever. It dictates the literal amount of its monetary units that exist on earth (another thing carefully defined and explained in Econ 101) by extending credit. It extends this credit with no collateral, no limits and no need for leverage. They create money when they want to for any reason, and they don't when they don't want to for any reason. They can, tomorrow, instruct the Fed to create $17T (roughly the national "debt") and credit it to whoever they want. The key difference between a central bank and all other entities: when it extends credit, it does not create a matching liability in the government's accounting. The central bank, or rather something with the power of a central bank, is the only entity in a society that can do this. That's what the "sole power to dictate the supply of money" means.
Any logic developed while thinking about debt carried by people, companies, cities or states, all of whom must add liabilities to their accounting books when they take on debt, does not apply to the entity that controls the central bank for the monetary units in question. Anytime anyone expresses concern about the national "debt" as if it wasn't something Congress could wave away with a pen in 15 minutes, they're being ignorant at best and disingenuous at worst.
It is absolutely critical that you read up on and understand this. It puts the lie to a lot of the national dialogue about austerity, belt-tightening, and service cuts.