You have a point (Himat beat me to it though) but more often than not, especially in aircraft design, the issue isn't a matter of "the material is lousy!" but rather "the person designing it either ignored something or was lazy and chose the wrong or not enough material to satisfy a need". If you're looking for impact resistance and crash survivability using the techniques available to a homebuilder, then carbon fiber probably isn't the right material for that application. At least not as the only fabric.... There's no reason- barring some issue of incompatibility that I'm not aware of- that you can't use different fabrics on different parts of the same aircraft to achieve different goals. They do it on commercially built aircraft.