Carson's a pretty good #6/7 type right now. Frankly the only reason he was waived is that he was the only dman on a two-way deal. Not a lot of upside to him but he's a good positional dman that's a surprisingly decent skater for his size.
edit: nope, Joslin's on one too. But the Canes had just acquired him.
don't understand why Atlanta would willingly take another piece of garbage
Well... they traded their number two center and numbers three and four are out due to injury. The team added Dvorak who makes forward-defense much better and Schremp who bumps Stapleton off the starting roster.
Would have really liked the Hawks to have claimed Carson, especially with the Hendry injury. Would have put less pressure on Bowman to pick up 2 D in trades.
I also would not have minded taking a flyer on Schremp and flanking him with defensively responsible wings like Hossa and either Brouwer or Kopecky. Give him a few games, see what he does playing on a playoff contender and see if he turns his stuff around finally playing for a contending team and with true leadership around him. But I understand this might not be the right time for a move like that.