How could someone like Paul McCartney, who wrote and recorded some of the finest rock music ever, write stuff like that? The "Talkin' 'Bout Freedom" song wasn't so hot either.
I think that by the late-60s, McCartney was such an established songwriter that no one would dare tell him that a song he wrote stunk.
I agree about the "Talkin' About Freedom" song. Just terrible. But, when he was writing it, he probably played it for somebody and asked their opinion, to which they sheepishly replied, "Oh, yeah. Sounds great, Paul."