well, that isn't totally apt, because an NFL team can play defense. "ducking" someone like that is quite lame, because you have to settle it on the field.
but fantasy football is more like golf than football in the respect that your scores are independent from each other, and there is nothing you can really do to prevent the other person from scoring.
sometimes a tank can be necessary, although it shows a complete lack of stones. I wouldn't necessarily do it, but then again, if it were for hundreds of dollars, I don't know.
I wouldn't call it "unethical" though. You are allowed to draft and field the team you want, provided you put in a valid lineup for your league.
what's next? vetoes for dumb draft picks? vetoes for questionable lineup decisions?
I think it is a slippery slope. The poitn isn't to win week 14, the point is to win the season.
NFL and MLB coaches always do this, to pretend otherwise is silly.
They don't tank to keep people out of playoffs (but then again, can actively play defense too), but they certainly don't always submit their strongest lineup. See teams that sit key players in out of conference matchups, or sit studs to get helathy for key games.
Do what you think gives you the best chance to win it all. But I think you should shy away from it for karmic reasons. If you are scared, get a dog. but play your team. you can't ever be sure of what happens in the playoffs anyway.