I think when bad things have good qualities, people still admire those good qualities while being wary of the bad ones. In this case, obsessive means that they

I think when bad things have good qualities, people still admire those good qualities while being wary of the bad ones. In this case, obsessive means that they put in effort that others wouldn't. It could lead to ruin, or it could reward them greatly. The bad part is the lack of detachment that lets them think about it logically, instead of being forced to just do it. Reward or ruin, they're going to do it either way.