For me it turns a legitimate best-on-best international tournament that has the potential over time, to become a prestigious event, into something that is along the lines of the NHL All-Star Game...something that is fun perhaps but is meaningless and has little prestige.
I would prefer that the NHL stay at the Olympics (it has built-in legitimacy) but don't mind the idea of a true World Cup. Just like football/soccer, rugby, cricket etc. if you make a proper tournament (qualifications, not invitations) then given enough time it has the potential to turn into a significant event with a lot of meaning, like the Rugby World Cup.
Once you change it from national teams, to adhoc all-star teams, it becomes nothing more than a series of friendlies/exhibition games. It loses legitimacy as a proper tournament to crown the best hockey nation. Lots of sports have World Cups and the format is pretty consistent, and they don't include all-star teams!