Ok, this is one I don't have 'the answer' for either, but, as Dana said, '...in order to advance our scientific understanding...'. It really comes down to this.
My opinion, which is required in this discussion, is that we have canine incisors for a reason and I value human life more than an animals. I don't think it's ok for some knucklehead to train his dog to fight, mostly because then it is a danger to humans, or to have a dog chained up in the yard and not cared for to the point that it has a collar buried in it's neck. However, on the contrary, I am appalled at the insane use of dollars to cater to frickin cats. They breed like rabbits, and are often left to multiply with the support of some knucklehead who feeds the feral population or, worse, has 20 or so in their nasty house.
I used to volunteer at the Virginia Beach SPCA. I saw countless dogs come in from some dumb-a** who bought the dog because it was 'cool' to have a pit bull and put a Harley bandana on it and look tough when walking around with it, but it turned out to be 'responsibility' and that's not fun. The dogs I saw, like most dogs, actually serve a purpose and are harder to replace than the average cat that allows you to pet it and feed it while offering nothing in return but a nasty litterbox to smell up some area of your house.
Dogs, I can see spending dollars and volunteer hours to save and rehabilitate for another owner or to be used, as I've seen work so well, to visit rehab hospitals and retirement homes and brighten the lives of people. The dollars wasted, in my opinion, on cats is absurd. Especially when replacing a cat is one the easiest tasks. Furthermore, the homeless cat population far exceeds the abilities of organizations such as the SPCA. They can rehabilitate one cat and one hundred more are being bred by some irresponsible little old lady down the street for the neighbors to, once again, corral and take to the SPCA, repeating the cycle of wasting the contributions of time and money.
It's all about the value we put on an animal. Again, assuming you isn't a vegetarian, your value of an animal makes all the difference. Cows and pigs and chickens are ok, but to think of a chinese restaurant, as the rumor goes, using cats and dogs is horrible. Why? Because they is our friends, or they is domesticated. I mean really, if a rat scurries across your baby's bedroom floor, would it incite a riot if you killed it with prejudice? Yet, if someone poked one with a needle to further Cancer research, then we have to question it's feelings.
Another opinion I have: I, to be honest, don't know how true it is but it sounds believable. A joke I have heard is, 'why do they use sterilized needles for lethal injections?' As I said, I don't know how true this is, but, regardless, I disagree with the whole lethal injection thing anyway. On the subject of this humane question, I think it' silly to worry about someone's feelings when you are about to kill them. Furthermore, if they are being killed, it is for some serious reason, like they killed and raped someone's loved one(s). Furthermore, again, I think it's insane to waste so many dollars when a box of .22 caliber rifle rounds can be had for $25/20. A simple stand-up shower stall shooting gallery with little down-angled stots around the walls for rifles and a drain to rinse it out after each use. It would still be quick an painless.
So, instead of an answer I just pose more questions, as I so often do because I'm not arrogant enough to presume to 'know' anything.
John