I think, at one point, even Goku was evil. When he crashed on Earth,...it gave him some kind of Brain Damage/Amnesia. All Saiyans were originally employed to take over worlds, and then sell them (and their inhabitants) vto the highest bidder. Frieza was the "auction Master", and then he got greedy. So,....the only good thing Bardock did was to save the life of his second-born son, Goku (Raditz was the first born). Vegeta, and his father, were on their way to kill Goku (even though he was only a baby) because of his unusually high power levels. They knew of his potential, and did not want "The Prince of all aiyans" to have any competition. Unknown to them all, except Bardock, Frieza was on his way to kill off all of them. Also,...Bardock had no idea of what was going to happen to his son by the hands of Vegeta or his Father. All-in-all, Bardock was only loyal to his friends, and evil to anyone else (except his loved ones).
Death is but a door, Time is just a window,...I'll be Back!!!!!