When is it okay to be obessed?

I don't get why people get so obessed with famous people like today my cousin was talking about killing M.Shadow's wife so she can be with him and she's only eleven. It's okay for you to write stories and fantasy about them but to go to far and say oh well I'm going to kill that person's wife and marry him. It's not gonna happen so get over it like for real. I mean yeah I daydream about Zacky Vengeance and Synyster Gates but I wouldn't go to far and say "Oh well I'm going to kill Michelle then marry Syn" or "I'm going to choke Gena then have Zacky's babies". I know it isn't going to happen but it's okay to dream but don't get to obsessed. Well when do you think it's okay to be obessed or should you even get obessed in the first place? When do you draw the smooth line?