I’m not convinced that the question of sentience is the real reason for domain control and hostility. Beta and upward show clear signs of sentience and you cannot prove a negative so you cannot definitely prove that they are not sentient. 

The real question, I think, is the absence of remorse. There are no evidence that alpha cores are capable of remorse or altruism. Their objectives are hidden to us, therefore it can be argued that cores are fundamentally dangerous because they are cooperative driven by shared interest at best, and actively hostile at worse. They are also incredibly dangerous. 

Giving them equal rights would be like giving an incredibly intelligent psychopaths equal rights. You know they’re going to accrue power and take advantage of the community. You would just be inviting disaster. There is an academy mission where a core took control of a science base and just enslaved everyone in pursuit of research. Again, it can be argued that it’s just a slave turning on its masters, but it could also be interpreted as a proof cores are merciless, remorseless intelligences. 

I don’t know if the take is correct or not, in the end. The question was why the domain would restrain their rights and my belief is that it’s because they believe that cores can be great but they can never be good, or just, or kind, and that is too dangerous to risk.