It's in the article. If you're not impressed by it then I'm indeed out of arguments.

Furthermore, while D and E seem plausible candidates for reasons against killing a being with these properties (E is in fact Peter Singer's view on the matter), none of the criteria from A to E seem relevant to suffering, to whether a being can be harmed or benefitted. The case for these being bottom-up morally relevant criteria for the relevance of suffering (or happiness) is very weak, to say the least.

Maybe that's the speciesist's central confusion, that the rationality/sapience of a being is somehow relevant for whether its suffering matters morally. Clearly, for us ourselves, this does not seem to be the case. If I was told that some evil scientist would first operate on my brain to (temporarily) lower my IQ and cognitive abilities, and then torture me afterwards, it is not like I will be less afraid of the torture or care less about averting it!

There's also a hyperlink in the first paragraph referring to section 6 of the linked paper.