I'd say it's easy to find oneself consumed by something when they entirely dedicate themselves to it and the lifestyle it promotes. That can definitely include different genres of music as well.
I don't even know how long I've been listening to metal. Maybe 12 years? It started with Down back in 1995 if I remember correctly.
The thing for me is that I don't dedicate myself to a genre of music. I don't dress what most metalheads would consider 'metal', I don't live a lifestyle most metalheads would consider 'metal', and thereby I don't confine my musical taste purely to what can be labeled "metal". Because of this, whatever interest I have in the genre, while being a part of my life, has never consumed me.
Another thing is that I'm extremely particular about the bands I like and choose to listen to. In my 12 years of listening to metal I've really gotten into, maybe, 7 or so bands (my all time favourite being Opeth, as I'm sure you can guess), although I've listened to pieces by innumerable others.
So, similar to the consumption of food, I would suggest that it's ultimately a matter of moderation. I can certainly see how metal can become toxic when it's all a person listens to.
Classical is fantastic, by the way. It was actually Yngwie Malmsteen's neo-classical work that piqued my interest in classical music, and I've become a rather avid fan of such composers as Bach, Paganini, and Mozart (despite the conspiracy theories
). I also very much like folk and traditional music - Paco de Lucía, Luar na Lubre, Milladoiro, Amalia Rodrigues, Sangre Cavallum (although I'm not sure how "traditional" or "folkish" they can be considered...), music of the various Hispanic cancioneiros, and so on and so forth.