Never, ever, ever intentionally throw a game in fantasy football. It's TERRIBLE for the competitive balance of the league. Ultimately, having a well-functioning, acrimony-free league is far more beneficial than trying to earn yourself a better round 1 playoff matchup.
bull####. it's no different than a team sitting their starters when they've already clinched home field. by tanking a game, they feel they have a better chance to win a championship.
if you think you can win by getting a better playoff matchup, go for it. if the league is concerned about it, change your playoff rules so the #1 team gets to choose their matchup.
If you're sitting Peyton Manning on your fantasy team because you think it lessens his chances of getting injured, I'd say you've got bigger problems than your first-round playoff matchup to worry about.
An NFL team resting starters to recover from existing injury and prevent future injury is not the same thing as tanking. The NFL team's GOAL is still to win the game. They're still trying their level best to win the game with the players they have on the field. They are not trying to lose. For example, see:
http://www.pro-football-reference.com/boxscores/200501020buf.htm
When a fantasy team "rests its starters", however, it is trying to lose. It wants to lose. Its goal is to lose. The ultimate, most desirable outcome is adding a loss in the loss column. That's why "resting starters" is not a very good NFL comparison.
A better NFL comparison would be if a terrible team started intentionally TRYING TO LOSE to improve its draft position. And the second anyone provides me with any examples of that happening, I'll warm to the idea that it's okay in fantasy, too. Good luck finding any, though, because
it doesn't happen. No NFL team intentionally tries to lose a game, even when losing that game is in their own best interest. Just look at Jacksonville, Tampa, and Atlanta in recent weeks, all getting key wins that give them nothing but might ultimately cost them a franchise player in the draft. Look at Houston giving all they have and nearly knocking off the mighty Patriots, despite Houston jockeying for the #1 pick and New England jockeying for the #1 seed. NFL teams never, ever, ever
intentionally try to lose. And neither should any fantasy team. Ever.