The main problem with obsessions is that they often come to an end. The end can be hurtful, or simply embarrassing. I once obsessed about collecting cow figurines, I am horrified that I even just wrote that. I also had a strange obsession with the 1950s, stickers and Ricky Martin, oh god, I need to stop. Obsessions with songs can lead to hatred. Obsessions with food can lead to disgust. Obsessions can lead to rehab.
The most dangerous obsession is people. You want nothing more than to do anything and everything for ever and ever with that person. You have the same dream every night, the one about you and your lover living in that lovely rambler together on that lovely culdesac, with those lovely kids, consumption is done in excess and and there are family photos on the mantle, and if its a good night you might even have a mini-van. One morning, as you wake, you sit up in your bed like always, eyes closed, arms stretched up, and POW, right in the kisser, you are smacked in the face by...something, you don't know what it is, its just different. Every night after that you no longer have that blissful dream that you had had for so many nights, instead you have dreams about unicorns, and the Rugrats.