When it comes to 'violence' in hockey, I find it's easiest to break it down into three distinct categories:

1) Fighting
2) 'Clean' contact
3) 'Dirty' contact

The fact is that any contact sport is going to have a bit from each category. As much as I think the visceral joy of hockey fights is great, I don't think the game would be doomed without them. However, I believe clean contact is absolutely essential. I've watched and played in games where checking was prohibited, and honestly it sucked. It's like hockey + roofies, or making the NFL into a touch football league.

When it comes to toning down NHL violence, I think the only category that qualifies is 'dirty' contact, best exemplified by the Todd Bertuzzi - Steve Moore incident. Keep the fights, keep the punishing body checks, but stop it somewhere short of causing disability :P. (Since Bertuzzi was suspended for the rest of the season, I'd say the keep-it-clean message came across pretty clearly)

I really have trouble believing that hockey has lost popularity because it is too violent. A hockey hit is like a football tackle, it just looks cooler because the guys are moving faster and often slamming into a wall :P. There are several proposed rules changes that intend to speed up the game and increase offensive production when/if the league returns. While this is a case where the damage has already been done, I think those types of changes would do much more good than trying to crack down on violence.