The music festival at Woodstock 50 years ago was a big deal. There had never been anything quite like it in America before — not in terms of size or caliber of performers (though Monterrey Pop might not have been too far behind in terms of the latter). But with the 50th anniversary approaching, it was inevitable that precincts of the mainstream media would make Woodstock out to be more than what it was. The heady combination of nostalgia and leftism would see to that. That combination outdid itself in a PBS program called “Woodstock: Three Days That Defined a...