The race doesn't' end on lap one ya know, so its not like Rosberg was fighting for the win. It is not a matter of dignity but a matter of race craft,IMO. Rosberg certainly did not look dignified in his interview I can tell you that!
See how Lewis smartly gave up his position in China? It's up to the driver to work out in his mind whether holding back the attackers will give an advantage after the first stint... In the case of a track like Bahrain, where it is one of the easiest tracks to overtake, compounded with the fact that Rosberg's rear end was sliding like a puppy on a tiled floor, the tactic of blocking in the first stint was never going to work out for him.