It's debatable how racist Branch Rickey himself might have been—he was born in 19th Century America, after all, so even if he were in, say, the least racist 10% of the white population of the time, he almost surely still engaged in a paternalism borne of the assurance of an entrenched superior racial status.
But it is also completely understandable that Rickey had to be very careful to choose the one black player who would be the most acceptable/least unacceptable to the out racists among his colleagues. There were any number of other players Rickey could have selected who would not have had the fortitude to withstand the brickbats of the first two years and, as importantly, to finally stand up for himself on the field starting in year three. That third year was crucial in the development of black player acceptance, because it paved the way for Jack and the others to be regarded as a player same as everyone else, and not just as a novelty colored player.
RIP Jackie Robinson.