The original three part pilot episode was a lot grimmer than the series that followed (original series), Zac getting killed, Adama and Apollo having a few seconds to get over that before the cylons arrive and kill everyone else they love too. There is civil unrest, miss treatment of prostitutes, and Baltar getting his throat slit when his usefulness had ended.
Sure when the series started Baltar was mysteriously alive again, and there was a robot dog, and most people had completely got over all the billions of people that had died, but the time wasnt right for a relentlessly grim sci fi show, that would be a few years later when Airwolf came along.