Hide your collection. 
The samething happened with me with respects to 
comic books. I just hid the fact that I was 
collecting, putting most of my books over at my
best friend's place. Since I wasn't flaunting the
fact that I wasn't listening to her, she eventually 
calmed down and stopped searching my room. 
Sometimes in a situation like this, when there is 
no middle ground, you should try and avoid the topic. As
much as you'd like to change them, they probably want
to change you. 

The perverse thing about this, is that being so 
adamant against it, they may just motivate you to dig in your
heels about it. They did a study about forbidden love
affairs, and it appears as though the more the parents
forbid the relationship, the more passionate the lovers 
became about each other.     

As for collecting cels, it's no dumber than those stupid
commerative plates, Princess Di memorabilia, tea cups,
cigar labels, pickle jars (they can go up to
$40 000), wedding cake, or match book covers people
collect. I tell myself this everytime I get a package.