“If the U. S. defaults on debt obligations (bonds), then there is no longer any moral obligation for taxpayers to pay taxes.”
Indeed, you will be able to comfort yourself with that in jail after having had any remaining assets seized by the IRS, who will be even MORE humorless than ever in collecting their due.
Notice I said moral obligations, not legal. But once their ability to shame people into paying taxes goes away, then seizure becomes all the more difficult.
Make no mistake, tax collections are essentially voluntary. If enough people say “no” to paying taxes, there is simply nothing government can do about it.