You're both right and wrong; Oryx still loves Crota in a familial capacity. Although they strive for strength, and value that in an extreme "survival of the fittest" model, the Book of Sorrows also indicates that -- despite all the want for killing each other -- they still love each other and have respect for anyone (even family) who can best them. So I would say you are right, but he also has that attachment to Crota that would spur him even more to attack the our system.