Unless in the very distant future, when it will be possible to simulate any biochemical experiment on a computer, just as now nuclear explosions or aerodynamics of aircraft, which have yet to be created, are simulated on a computer.
Today But the biology of animals (especially the biochemistry of cells) has been categorically insufficiently studied, therefore, there are no alternatives to testing new drugs on animals with subsequent dissection and analysis of their organs under a microscope.
At the same time, the scientists themselves do not bring any killing of laboratory animals pleasure, they are normal people, not flayers. It's just that the logic works here "it's better to let a hundred mice die now, but then save one person." And scientists do not agree with the choice of radical animal rights activists "and we do not care about this person."
I believe that this can be done now, but people do not want to test cosmetics / chemicals on other people, they think that animals do not deserve the same rights as people. But if you consider how biochemistry develops, then alternatives to this cruelty may appear. Although it cannot be denied that in order for this to end, many more sacrifices must be made.