When does it become an idol?

I believe a gun becomes an idol when the following conditions prevail:
1. An owner believes there are no circumstances when a regulation or restriction for public safety should be placed upon it.
2. An owner believes that guns don’t kill; they only save lives.
3. An owner has no doubt that guns preserve America’s most cherished values.—America and Its Guns: A Theological Expose, page 21

<idle musing>
A good start, anyway. I would probably add a few more, but they would just expand on these three.
</idle musing>