Lets see pretty well all of Trek, Specialized, Giant, Cannondale Santa Cruz, IBIS, etc etc. highest level XC and all mountain MTB's are carbon.
I work at a dealership for one of the brands you mentioned, and the ratio of broken carbon frames to broken metal frames is very high in real life. Causes vary, but that's the bottom line from years of firsthand work on hundreds of them.
We have one in the shop right now that's cracking in two places where frame tubes took routine impacts from spills. And I'm talking XC-rider spills, not spectacular freeride bailouts. On an aluminum bike, these impacts would just be routine used-bike scratches, not a cause for structural compromise. The warranty department declined coverage because the bike had taken hits in those locations (as evidenced by the scratches in the paint).
If you like carbon and you're not fazed by this sort of thing, then by all means buy it. If you want something that's going to shrug off crash impact, then
caveat emptor.