Player choice vs competitive play

Just now I was queued with a player that was supposed to go support and selected Camille. I guess the adc lolskilled the player to see if he was playing some cool new build or whatever and saw that support Camille had a 29% win rate and terrible stats. When he was asked to play something different he threatened to intentionally feed and picked Nasus support when our adc banned Camille, and his win rate for that champ was.... he never played him. Now I'm all for player choice and being able to play champs you have a bad win rate with, because from time to time I pick a champ that I had a couple bad games with, but this was more of a 100 games of straight feed kind of player, not the guy who picks a champ to counter someone and ends up not doing well. I have mixed feelings about stat-based choices, because I guess it's their right to climb with what they want to, regardless of how well they play with that champ, but the guy was pretty toxic about his choice being denied to him. Now, most of the time, banning someone's selected champion can be a bad move, but with such a low winrate it seems hard to really determine what should be done. I don't look at other people's stats over a small amount of games, but the more games played, the larger the stat pool becomes and the harder it is to determine whether the player is actually trying to climb, rather than trying to master a champion they just can't seem to grasp in a ranked game, for added challenge. What are your thoughts? Let 'em play 0/12 support Camille to the end of their days, or ban the champion and risk having them threaten to intentionally feed? (Has happened 9/10 times in my elo)