I don't even have an argument with you because you have a consistent view on the issue, unlike those that eat pigs but not cats or dogs. So we're actually mostly in agreement, the arbitrary classification that people are making with pigs and dogs being food or pets is silly.
And no, breeding compatibility does not decide my diet.
Edit: Your third and final paragraphs were added after I started writing my comment, which is why I didn't address them. I also don't understand your fourth paragraph.
As my third paragraph states, there are enough exceptions to see that species isn't always that definition, and that it is somewhat arbitrary.
Fourth paragraph is also an additional information for those who want to rank horses as lesser beings because we are obviously capable of reigning the planet thus our evolutionary path is more worth - without noticing that the evolution and natural selection don't have a goal set in stone.
If you don't have an argument, then why laugh at me with that horse joke? It's entirely irrelevant and, given my following comment, incorrect.
Species however has a scientific definition - "A species is often defined as the largest group of organisms where two individuals are capable of reproducing fertile offspring." Thus not a social construct, this is a well defined classification. We may reclassify species based on new information or because they evolved, but that doesn't mean its a social construct.
Ranking them by importance is social, however.
Evolution is gradual, there are no big species jumps.
What was there between sapiens and erectus, X? What was between sapiens and X, and X and erectus, Y and Z?
What was then between sapiens and Y, Y and X, X and Z, Z and erectus?
This can go on forever, evolution is by nature gradual, lets say it in your terms, a regression is more suitable than classification.
What point in this finely continous line do we pick for discrimination? Speciesism discovered!
If you find the theory of evolution a fact, then you wouldn't laugh at me. Any rational evolutionary biologist will agree that species are here to simplify the conversations, they cannot be used for ranking which species are better - they are also not the main theme of research.
Do you know how species are defined? Sane definition? - members of the same species can produce a fertile offspring. But there are hundreds if not thousand of exceptions where this happens even across the species boundary - the reason why it happens is that our labeling is in its core subjective and somewhat arbitrary, there's no dividng line/plane/svm-hyperplane.
In the parallel lines of time in evolution and natural selection we've been as long as all the living beings.
You wouldn't find homo erectus (neanderthalensis, habilis, rudolfensis, ergaster, floresiensis, even some australopithecae) attractive but you could procreate. There's a biological reason why you can't have children with a horse, it's not a species reason, it's not even ingrained in our species labeling as can be seen from the above definition.
What, you would rank the being as irrelevant (or less relevant) if you can't have children with it? Comedy of irrationality.
Go try finding your rationality and get back to us on that.