Animal experimentation is horrible and terrible. Even in the most ethical of studies suffering is inflicted upon animals that otherwise would not have happened; entire genotypes of animals doomed to additional suffering have been bred in some cases. But the alternative is far worse: to not perform these animal studies, or rather for some privileged group to use force to prevent others from performing such studies, and so bring progress in medicine to a grinding halt. Without animal studies there would be no new meaningful advances in medical science. It is a harsh and unpleasant aspect of the human condition that forcing suffering upon animals in the course of scientific studies is necessary to advance both human and veterinary medicine. A few suffer for the benefit of many - an equation that should make any sane and compassionate person uncomfortable.
Animal studies are even required to refine the science needed to move beyond animal studies. Ethics and morality aside, studies employing animals are expensive and time-consuming. Given the choice, scientists would much rather experiment on cells in a dish, or on slabs of unfeeling cultured tissue, or upon simulations of animals, if these methods would generate results of the same quality.
In comparison to what might be and what is possible, we live in a barbaric age of suffering, war, death, and sundry other horrors that we like to keep behind the curtains and out of the mind's eye. But barbaric as it is, this age is far better than the past by all such measures. We no longer absolutely, definitely need to slaughter animals for food to sustain the populace, for example, and rates of violence between humans are far lower than in the pre-modern era of tribes and universal poverty. The option stands open today for a society of vegetarians: it is practical from a technological and economic standpoint. That we have not moved rapidly in that direction is our shame, and our descendants will look back on us as savages for this and many other reasons.
Those people who criticize and take action against the use of animals in medical research should first look to their diets, and then to the practice of farming animals. Vast and expansive animal suffering is caused in the name of putting meat into the marketplace - greater many times over each month than in all the animal experiments in modern history. Persuade the omnivores of the human race to relinquish their participation in the meat market before savaging the medical science that will benefit both man and beast.
In short, the human condition is a rotted, cloying swamp, but we're closer to the edge than we were - no longer up to our necks in it, we now have the luxury of finding more of our surroundings to be disgusting and primitive. The way out to solid ground is forward, through more of the same, until our biotechnology becomes good enough to do away with the suffering we must inflict upon animals in order to build better medicine. Perhaps along the way, societies will arise whose members also reject the needless suffering we presently choose to inflict upon animals in order to eat the same diet as our ancestors.