You can remind yourself, as you're up in the air, that you are safer than if you were on the LA Freeway, or whatever road you happen to drive. That's a great question. I don't think it is altogether ghoulish. I think we genuinely want to know what happened to these people out of concern. And, yes, there is a part of most of us that want to SEE the disaster, in all its details.
People stop to look at car accidents for the same reason.
That's another great question. You can't stop thinking about something by telling yourself to stop. What you can do is distract your mind, change sets, so to speak. Get up from your seat, walk down to the lavatory, and walk back. Do the crossword puzzle in the in-flight magazine.