They are usually the worst players on the roster, aside from the 4th liners. It's normal that they receive more hate than their top 4 teammates, because they rarely have a big positive impact on the game. More often than not, they're just out there to let the top 4 rest.
For the Caps, Orpik is the player that the fans would like to see leave the most. And Schmidt, we cut him more slack because he's young but some days he's atrocious in his own end.