Yea, I could realistically imagine it working and functioning where they kill each other once they've past their usefulness. Or they kill those who are unfit to reproduce, or those with predisposition to be excessively nice, or kind. In their environment being nice might not be productive. Why does that prevent them from developing technology? Maybe they reproduce every month and grow much faster and live much longer. Maybe they do not sleep. Maybe their system has a binary star causing no nighttime, or perhaps they go through long periods of darkness. I don't see why this would prevent a social evolution to emerge. Most of the life that has ever existed is now extinct. Is that because of the golden rule? I think it's because of the environment, lack of food, etc.
The idea that there is a golden universal rule seems more like the idea that the world is flat. It's centered on us, I don't think this golden rule is what we think it is. We don't even follow our own golden rule and yet we're successful. What we are is far from perfect, but we don't want to change. We're not even what we once were, who is to say what is optimal?
Would they have a respect for intelligent life? Probably. But why? Because they might see see similarities in that we both reproduce through a natural selection & have developed a sub-conscious and a conscious mind able to simulate and make more complicated decisions past a threshold that they consider intelligent. We might not even be close to that threshold. This respect would be selfish in that there's a similarity, and maybe we both like that. But that doesn't mean they would necessarily feel bad about killing us. And if we thought they were a danger, we'd probably kill them. Selfish. Just because we might feel bad about the lost opportunity doesn't mean much to me. Our desire to reach out and contact other's seems to stem from our generally social nature. In a way, even that is selfish.
A more advanced form of morality might say that sending advanced knowledge by radio to another independently developed life form could be a bad thing leading to their destruction (Prime Directive). What a waste all those millions of years of evolution would be if we caused some other world to prematurely go extinct as a result of learning about technology they were not ready for.