We live in a world, unfortunately, in which human monsters come in many forms. I say unfortunately, because sometimes the person next door, who looks like us, may be a monster. This means that we may be especially unlikely to see the monster coming - and to avoid the awful harm that ensues.
The Rolling Stone cover - in addition to its well-researched, thoughtful article - makes this point very well. The MySpace photo of Dzhokhar Tsarnaev shows what looks for all the world like what a kid his age wants to look like - try to look cool, trying to impress girls. Blowing up innocent people at the Boston Marathon looks like it would be the last thing on his mind. But that's what he apparently did, and that's why it's so important to call attention to this seeming disconnect between attractive image and deadly deed.
It's not as if magazines never put photos of terrible people on their covers. Adolf Hitler was Time magazine's "Man of the Year" in 1938, followed in 1939 by Joseph Stalin. Time put them there not because they were good or remotely admirable. Time put them there because of the bad impact they were already having on their countries and the world.
The notion that Rolling Stone was trying to glorify Tsarnaev is about as logical as Time magazine was trying to glorify Hitler. Rather, in both cases, the magazines were doing their job: bringing details of monsters to us, so we could better understand them, so we could perhaps recognize what they are in the future, before they commit their atrocities.