Actually, they've stated it's impossible to extend the arm in a punching motion without raising the elbow. That's demonstrably false. If you don't extend the arm, sure, but that's not going to cover much of a punch.That's hard for me to judge, as I don't punch that way. But I can say that LFJ doesn't seem to have asserted anything that is demonstrably false. Others, who have suggested that it is impossible, have asserted something that is demonstrably false.
From a lay perspective, the people who are making overblown claims that can be shown to be false are the ones losing credibility.
Or to put it similarly to how Juany did, I say, "an object at rest stays at rest," and you say, "Nuh uh. That's impossible." Who's credible?
LFJ says you can extend an arm while keeping the elbow down. He provides a simple, easily conducted experiment to demonstrate what he means. Other people say (and please picture Luke Skywalker responding to Darth Vader on Cloud City), "No. No. That's not true. That's impossible!"
Guy B: Search your feelings, you *know* it to be true!
Nobody Important: [anguished] No! No! "