The argument is one of economic convenience. Caring about model welfare slows us down or makes it more expensive, just like animal welfare and not having slavery...

And there's a blurry line here. Obviously slavery is abhorrent, and animal abuse is bad, and factory farming often crosses the line into animal abuse and we should accept that chicken will cost ~25% more per pound to have the chickens be able to walk around a little bit... but how do we decide when a computer system is worthy of respect? Convenient not to think about that.