How do I build a mast out of Carbon Fiber or glass

The stability factor is a two-edged sword. Mike Johns is right in that a heavier mast adds to roll moment of inertia, and Sorenfdk is right in that a lighter mast reduces pitching. The high roll moment of inertia makes the boat harder to roll over in waves, although it will heel more in normal sailing conditions.

As for carbon fiber masts being trendy, detrimental, and expensive, well what's wrong with being trendy--Nothing. Will it be detrimental? Maybe, maybe not. It depends on the hull design and the location of the boat's center of gravity with either mast. Will it be expensive? Unfortunately, yes, the price of carbon is still high enough, and the labor required still specialized enough, that carbon spars are more expensive than aluminum ones.

Eric