Brock Huard had some thoughts on the Hawks and Nkemdiche and I think he sold me.
One, the Hawks defensive line room has a unique combination of players that could be very successful at motivating him. Mentioned if he was a WR or RB or OL, he wouldn't make this pick, but the defensive line room run by Bennett, Avril, and potentially Clemons would keep Nkemdiche in line.
Two, the Hawks will have a very good chance to get very good players at 56, 90, and 97, but you rarely have a chance to get someone with the potential for greatness. Obviously there are a lot of red flags, or else he wouldn't be there at 26, but if you trust PC/JS to come away with players at 56, 90, and 97, they are in a position to gamble on a lottery ticket at 26.