Some people will never accept Krug because he is not a rugged, physical penalty killer. They simply look past the role and skill he adds to the team, none of which is to be an elite shutdown defensive defenceman. He has flaws. He has deficits, but they are much easier to make up for than finding a guy who will give you that level of production on the back-end.
Personally, I thought he and McQuaid played a lot better than he and Carlo play together. The defensive flaws are much more noticeable because they have been putting themselves into more bad positions than a more experienced defensive pair. If its up to me, I keep him and Carlo together and hope that over time they learn how to improve their play as a pairing in their own end. If that doesn't happen, there are a few options to perhaps put the players into a better position.
Chara-Carlo
Krug-McAvoy
Gryz-Miller
Chara-McAvoy
Krug-McQuaid
Gryz-Carlo
No need for a Marco Scandella, who will make us a little better defensively and a lot worse offensively. I also believe Krug is a huge part of the chemistry that has let this team gel and succeed this year, and that trading him would be a major step-back in that regard.