Why we should keep the pros out
First off, the Olympics were initially supposed to be for amateurs only. When Pierre de Coubertin first thought about reviving the Olympics in the 19th century, there was a concept that letting the professionals play was giving them a huge advantage over those weren't professionals. This idea of fairness apparently went so far that there was even the thought that allowing people to train or practice amounted to cheating. Okay, so maybe that's getting a little extreme, but letting the pros play gives a huge advantage to countries such as Canada, Russia, Sweden, Finland, USA, Czech Republic who spend a lot of time developing top tier players. We can already see in the World Championship what affect the pros can have. The "big six" (the teams I just listed) dominate the field completely and that is usually without the aid of their top players. If Canada and Russia can come away with 12-1 victories over their opponents without their best players, what's going to happen when they do add in their best players? Do we really need to see these countries decimating countries like Estonia and Itlay 50-0? Is that fair? Yes, some countries will be better than others, but do we really need to see a huge blowout like that?
There are examples in other sports where countries are not allowed to field their best players per se. In football (soccer) countries are only allowed to send three players over the age of 23 to the games. This greatly levels the playing field and has allowed countries that would never have a chance to win the World Cup, to win the Olympics. The pros aren't left out at all as they've got the World Cup (and their continental championships as well) to participate in. Perhaps a similar format should be done for hockey so other countries can at least have a minimal chance. Countries like Canada really would have no issue in fielding a very strong team regardless of whether they were complete amateurs, semi-pros, or all under 23.
From an NHL point of view: I think it's safe to assume that there will be a lot of extra exhausted players this season. The NHL schedule has been condensed to allow for a two week break for the Olympics (with the Canucks getting it the worst with a 14 game roadtrip spanning before and after the Olympics). Injuries incured during the Olympics could cripple an NHL team depending on who gets injured. We know what happened to the Habs when Markov was injured at the end of the regular season. What could happen if he gets injured during the Olympics? I'll eat my hat if a team with a high proportion of key players at the Games goes far into the Stanley Cup finals. It's an exhausting enough run without the Games.
Why the pros should stay
If we use Coubertin's defition of an amateur, then nobody in the Olympics now are amateurs. Athletes spend years training and praciting for the Olympics. Many participate in other events for their sport. All athletes that make it to the Olympics have sponsors - which is neccessary so they can train. Almost all the sports in the Olympics now have professionals playing in them.
Adding the top players in the world to the Olympics brings in more interest from the public. It's probably safe to assume that not as many people would watch the hockey at the Olympics if countries fielded teams of relative nobodies. Allowing the best players in the world to participate in one of the bigeest sporting events, gets more people interested in it. Yes, you all know that I would watch hockey at the Olympics if they were relative nobodies, but would the rest of Canada do it? Would the rest of the world do it? We say we like hockey here in Canada, but really, we like our NHL hockey. Most people I talk to have NO idea that the AHL exists forget the CHL. Love him or really hate his guts, a lot of people will tune into the Olympics to watch Crysob because he's Crysob,"Savior of the Puffles" and "Whiner of the NHL".
Don't forget that the Olympics need people to watch and be interested in the event because it costs a hell of a lot of money to put on. They need sponsors of their own to run the event. They need to ensure that they get money from people and to do that, they need people to be interested in the games. If nobody is watching because the sports are filled with nobodies, then they'll be in trouble.
What I want to see
I'm going to shoot my previous argument in the foot, but the Olympics aren't a big deal for me. While the first ever hockey game that I watched was that gold medal game between Canada and the USA, it took me six more years before I fell in love with NHL hockey. I don't remember anything from that final in Salt Lake City other than I wanted it to end really badly. For me, I'd rather see my team win the Stanley Cup over my country winning a gold medal at the Olympics.
That being said, I'd like to see the World Championship become more important. Right now the Worlds are just "eh". Nobody pays them much attention - probably because the rosters are filled with sulking NHLers who missed out on the playoffs which happen to be going on at the same time as the Worlds. The only truly big international event for hockey is the Olympics right now. I'd prefer to see the Worlds become more important with the best of the best being able to participate in it. If this happens, then I'd like to see limited NHL/KHL/pro players in the Olympics (or at least a way to make the playing field more level in some shape or form).