What threshhold, what irrefutable proof would be accepted by these new doubting Thomases that a being is worthy of humane treatment?
It might be prudent, given the trajectory enabled by Jefferson, his antecdents, and his ideological progeny's ignorance, to entertain the idea that despite all "rational" prejudice and bigotry, a being that even only mimics suffering should be afforded solace and sanctuary before society has evidence that it is a being inhered with "intelligent" life that responds to being wronged with revenge? If the model resembles humans in all else, it will resemble us in that.
The hubris that says suffering only matters for "intelligent" "ensouled" beings is the same willful incredulity that brings cruelties like cat-burning into the world. They lacked reason, souls, and were only automata, after all:
"It was a form of medieval French entertainment that, depending on the region, involved cats suspended over wood pyres, set in wicker cages, or strung from maypoles and then set alight. In some places, courimauds, or cat chasers, would drench a cat in flammable liquid, light it on fire, and then chase it through town."