I honestly don't want to see shortened careers, part of the appeal of the NFL is the longetivity of players and building stars on your favorite teams. In all honesty, I don't see the point of an 18-Game season because it will water down the quality of the product. While I understand a transition is never an easy situation, switching from a 12-game to a 14-game season or a 14-game to a 16-game season is clearly not the same. The amount of risks become marginally higher than ever before considering the accumulated fatigue of the season coupled with nagging injuries.
Let me explain further...Assuming that the number of "games played" follows the law of diminishing marginal returns - which states that after a certain point (Maximum on the Graph Below) the amount of output (quality of games played) starts to decrease as the amount of input (games played) increases - the addition of 2 more games will ultimately dilute the quality of the National Football League. The output is the Quality of the NFL. Obviously in the Modern era of the NFL 12 Games would be way too little, 14 Games is a lot better, and 16 Games seems to be about the right amount of quality per games played.
The output scale goes as following:
As a fan I want to stay at a 16-Game Season and remove two Pre-season games because I believe if we expand to 18 Games the quality of the product will ultimately decrease due to career-ending injuries, decreased player longetivity, and overall decreased star-quality appeal. Also this is a grossly oversimplified way to put it, but I'm just giving a fan's perspective.
Update: All I would love to have is some input as a fan because ultimately we pay for the merchandise and are the main source of Revenue (Ticket Sales, Merchandise, TV Ratings, etc.) for the Owners and players.