> the only thing removing category distinctions here will do for you is give license to treat any organism however you wish
This is only true if what stops you from treating certain organisms in a certain way are these objective category distinctions (rather than the approximate ones your brain makes), but I don't think that's generally how it works. People who wish to harm others will harm others regardless, the only thing that will stop them is consequences. On the other hand, people who don't wish harm to others will not harm others regardless of whether they believe objective categories or objective morality exists.
> People who wish to harm others will harm others regardless, the only thing that will stop them is consequences. On the other hand, people who don't wish harm to others will not harm others regardless of whether they believe objective categories or objective morality exists.
This discounts that there are those who wish to harm others who aim to persuade others still to look the other way or even join in on the harm. If the only argument against them is that they'll face consequences, they only have to grow their numbers large enough to avoid said consequences.
To say nothing of those who'll argue against there being any consequences in the first place.
This is only true if what stops you from treating certain organisms in a certain way are these objective category distinctions (rather than the approximate ones your brain makes), but I don't think that's generally how it works. People who wish to harm others will harm others regardless, the only thing that will stop them is consequences. On the other hand, people who don't wish harm to others will not harm others regardless of whether they believe objective categories or objective morality exists.