He's not killing the Nuggets. The Nuggets' complete lack of any inside offensive game, the Nuggets' general aversion to defense, as best evidenced by Carmelo doing nothing and Iverson constantly gambling for steals, the total lack of accountability, teamwork or camaraderie - that's what's "killing" the Nuggets. But don't forget, they did win 50 games last year, so he couldn't have killed them that badly. I agree he's a backup point guard being unfairly thrust into the role of a starting point guard, but that's not his fault - that's the Nuggets' fault. It's part of them being an inept team; their shortcomings are not the fault of Carter.
I don't see the chucker thing either. Last year, he took 6.8 shots a game in 28 minutes. One shot every 4 minutes is very few for a starting point guard (Sam took 7.6 shots a game in 17.5 minutes with Boston, and 10.6 in 25.7 with the Clippers). Carter also had an assist to turnover ratio above 3 (5.5 assists to 1.8 TO) along with 1.5 steals per game, 46% shooting and 35% from 3. He hasn't been a great shooter, but he has always been a good ballhandler who makes few mistakes. While no longer a great man defender, he's been a good defender throughout his career and I think he would excel in a team defensive strategy. So I definitely don't think he's a bad player.
Of course, his weakest point, shooting, is also Rondo's weakest point, and House (and Cassell) both showed at times how important it is to have our backup point spread the floor. So he's not an ideal fit. Still, if he is/was available for the veterans' minimum, I don't see why we don't/didn't take a shot on him.