Feeding VS Doing Nothing.
Okay, so, let's say you have someone feeding on your team, doesn't matter what their feeding let's just say they have an awful score. But on the bright side they still come to teamfight's, help get objectives, keep up in CS and overall are trying to win. But on the same team you have someone with a good score, great CS, didn't feed lane at all but they won't follow up on ganks, they won't go for objectives, they're never in a team fight and they constantly refuse to help the team win.
Which is worse? In my opinion, it's the second one, i'd rather have to fight a 5v5 with a fed enemy than to have to fight 4v5 all game with no one fed.
PS: This is made much, much worse when it's your ADC doing either of these.