The reason that I wouldn't call him a 'peer' is that he is made and not of the same 'stuff' as his makers. All droids are also not equal, in that the mouse droids and buzz droids don't seem to be on the same level. They're in servitude much as any tool that we create serves us- but at what point does that level of sentience imply slavery? Especially if this is what they are made to do?
I think I might avoid any argument about slavery that goes down that particular line. There's little difference between what someone is "made to do" and "born to do" when people are born into slavery.
I don't think that holds up in a universe as diverse as that of Star Wars with all sorts of wild sentient beings. Particularly as most of the droids we've seen are of approximately human intelligence and surprisingly human mindsets. Whatever the secrets behind their construction, they're ending up seeming very human-like. So in terms of their intelligence and way of thinking they're more "peers" of humanity than some of the other aliens are!
I think that's a more important point. There probably is a dividing line. Where exactly that would be something for the droids to determine, probably. They'd have a better idea than humans would.
As @billd91 says that's 100% been argued to be the case about humans, like repeatedly, for centuries. It doesn't really matter why something exists if it's inherently sentient, sapient, and free-willed. You also can really get into the weeds with that because some droids will not have been created to be slaves (c.f. C3PO), but are clearly treated as slaves anyway.
There is a very big difference. Made being 'manufactured' as any tool. Born is not a manufacture process.
Been argued disingenously. They had no part in the creation - we can't create life. We can create computers, machinery, robots and at some point one things that they might develop sentience. But they are still not self-replicating. At what point does machinery==life? Even if behaviors and such are hardwired, they're still created, no matter the differentiation that it's not code.
How about the clones created on Kamino? They were "manufactured" but also definitely counted as life since they were, pretty much, just modified humans born, raised, and educated via a manufacturing process. Definitely as sentient as any other humans. Were they slaves? If no, why not? If yes, what's the difference between them and sentient droids?
They were created from sentient life. They weren't parts created for machinery, but replicated children, force grown, genetically altered humans. There's a difference between cloning and manufacture.
If the products of childbirth, cloning, and manufacture are all sentient, why should the process matter? It seems to me like you're positing some kind of inherent hierarchy between the different methods because of, what, raw material?
I'm saying that they aren't peers. If my computer became sentient at some point, that wouldn't make it de facto my peer. If someone clones a human then by the very nature of cloning it is still a human. Same with birth by the biological processes.