Perhaps the better question is, if Neanderthals were to somehow come back and enter the modern world, would we accept extending some sort of ethical consideration to them? I think we undoubtedly would.
The current deficient of other species that we all accept as special in some way in no way suggests that inter-species relationships of that sort are impossible.
Some people think neanderthals and humans mixed genes.
> the project published their results in the May 2010 journal Science detailing an initial draft of the Neanderthal genome based on the analysis of four billion base pairs of Neanderthal DNA. The study determined that some mixture of genes occurred between Neanderthals and anatomically modern humans and presented evidence that elements of their genome remain in that of non-African modern humans.
But some people think this genetic overlap is the result of a common ancestor, and not from interbreeding.
We give special consideration to primates - not just because they're rare but because they're close relatives to humans. Vivisection is limited pretty strictly if you're using non-human primates.
Would there be much difference between a chimp and a neanderthal? Neanderthals had the FOXp2 gene, and a hyoid bone, so they might have had language. Hunting is a complex activity, and so there's strong possibility that they needed language.
I guess having a language would be enough to guarantee extra protections?
(Having said all this, modern humans happily butcher each other every day, so who knows what'll happen for dolphins or hypothetical Neanderthals.)
Carve out a new nation of only Neanderthal, and I suspect we will go at it like we were making up for old time. Pop a few Neanderthal down in the middle of London, raising the first few to be familiar with human civilization (to the extent that this may be possible), and I would be a bit more optimistic about the outcome.
How we treat others seems to have a lot more to do with context than merit.