They don’t. And they don’t need to! Being rude at people who disagree with the US State departments official position (which is not propaganda) is good enough, because propaganda = opinions that are not in line with the US state dept.
They believe that “fact” so powerfully that theyll get angry at you and insult you. Other facts become unnecessary if the person saying them is untrustworthy. Uncomfortable truths, any thoughts about the US’s many, many efforts to control the global south may be terminated along with the messenger.
Besides people use Ad hominem because it’s just so easy