I think the point would be that the human test subjects make an informed choice to participate, while the rats have no say.

Personally, I like to think that karma will take care of those who treat critters - including fellow humans - poorly.

I think the human test subjects are prisoners, homeless and soldiers. Not much free choice in those 3 groups. As for informed choice, I think it goes some thing like this: "What's in this shot?" "Shut up and get your lunch. Next!"

A little lyrical interlude from comedy genius, Heywood Banks:

On the day the cartoon animals
reverted to their natural state
all the kids agree, twas a sight to see
when they peeled off the paper and they all ran free

On the day the cartoon animals
reverted to their natural work
they threw off their anthropomorphic ways
and totally went berserk

(chorus)

And there was. . .
Smokey the bear, choking on a camper
Smokey the bear, choking on a camper
Smokey the bear, choking on a camper
Bugs Bunny's in the laboratory, testing mascara

(verse)
Well there's old Mickey, that dirty old rat
Got a mouth full of cheese, and his head in a trap
Donald's in a Chinese restaraunt booth
with a ginger glaze and no sailor suit

(repeat chorus)

Well Rocky is a roadkill squirrel surprise
(Only flying being done is being done by flies)
Bullwinkle's in the woods, far away from here
with a radio collar and a tag in his ear

(Chorus/tags)

Porky smells nice around a spiral slicer. . . .
Goofy's sniffing out--drugs at the border. . .

(end)

I dunno, Elvira manages OK!

Another problem is that rats have faster metabolisims (sp) and can be bred to check for defects passed onto the hereditary line.