Cost. No doubt about it. It's what is killing the goose. Equipment, green fees, dues, whatever, cost is what is causing people to leave the game or not get started at all. Ask yourself the question: why should I pay all this money so that every golf pro and college golfer can get free equipment, greens fees, travel, etc., and even a second rate tour pro can earn $1,000,000 per year?
Expectations drive up costs, expectations about course conditions particularly.
The tour is killing the game by promoting its members as celebrities. The regular golfer can't relate anymore- not like they could in years past. And by the way, these "celebrities" don't even try to relate to the fans. Who was the last guy onm the PGA tour thagt really made an effort to relate? Peter Jacobson, maybe?
Slow play is a close second, but I'll tell you that lots of people will enjoy a five hour round for thiry bucks, but not for $75 or more.
I know what the media says and its effect on people's opinions, but in my humble opinion, based on their effect on the health of the game, I'd rank distance far behind cost, inability of the regualr golfer to identify with or relate to golf "celebrities," and pace of play as the most important issue.