The only thing "wrong" with copper as opposed to brass is weight. But in the small amount we use on large planes that isn't a problem. If brass was of the same wall thickness we might feel differently about brass. The only reason to use brass IMO is for bushings or where you need an assembly to maintain it's "roundness" and "staightness". Copper is so much easier to use. Because is has a thicker wall it is much easier to silver solder as it won't burn through as will thin wall brass.

Bish