@Thomas,
Attributing differing levels of value to human life based on what that person may or may not be able to contribute to my welfare (individually or as a member of society) is morally repugnant to me.
That is something that on a very basic, fundamental and visceral level offends my own particular moral compass.
And it is not that the humane treatment of animals in and of itself that diminishes human rights- it is the thought that an animal might possibly be held in equal esteem as any human being that diminishes the respect and innate value that should (in my opinion) be accorded all humans - regardless of their age or cognitive ability- or in other words, what they might be able to contribute to me or society.
The fact that they are human infuses their existence with more 'sacred' worth than that of any animal.
Anyway, that's what my moral compass tells me. It's offensive to my moral compass to compare a baby or mentally handicapped person to a cat.
Is your life worth more than mine because you might be smarter than me?
Is my life worth more than someone else's because I might be smarter than them?
Do people really measure the worth of other people based on what those people might do for them (again, as individuals or as members of society)?
That's a pretty scary thought.
My fundamental moral compass compels me to view all human life as equally sacred, and as such, deserving of the same rights, respect and treatment I would expect for myself.