Is animal experimentation ever justified?
Yes, unless you want you, your spouse, your child, other loved ones, or the general public to be the test animals.
(Animal testing is *highly* regulated and designed to minimize numbers used, and minimize or eliminate pain and suffering as much as possible, but it still involves the (humane) deaths of animals. And there is always non-animal screening prior to any whole animal use.)
No one wants to torture animals when doing animal research. I've done animal research, and I know how much regulation there is, and some of the measures taken to reduce numbers, and minimize pain and suffering.
I trained in a field (genetic toxicology) that was intended to replace whole-animal research (as much as possible) with other systems, for genetics related work - using cell culture, bacteria, yeast, plants, and computer modeling. But all that is insufficient in itself, unless you want humans to be the first test animals.
How about if human lives are at stake? We have made great leaps in cancer research by experimenting on animals. I thinks millions of human lives are worth more than some lab rats.
I don't think torturing animals is ok even then.