There are a variety of reasons why scientists experiment with animals ranging from cosmetic to behavioural and pharmaceutical. I believe that some of these are easier to justify than others but there are also alternatives to animal testing that need to be developed further.
One reason for testing on animals is for the development of new cosmetics. This sector has generated a great deal more criticism than others as it is much more superficial. Critics argue that these new products are largely unnecessary and that the suffering of animals does not justify the end product. Furthermore there are many cosmetics that have been developed without the need for animal tests.
Another of the most common reasons for animal testing is the development of new drugs. These drugs can then be used to treat both animals and humans. Indeed, many chronic illnesses are now treatable because of animal testing and it is for this reason that proponents of animal testing argue that it is so vital. However, this is a subjective argument as it values the lives of humans above the suffering of animals.
These arguments relate solely to animal testing, however there are alternatives to this currently being researched. Over the last few years there have been scientific breakthroughs with regards to improvements in testing on cells and human tissue. If these were to be extended there would be no need for any animals to suffer. Another possibility is to use computer models to test new items.
In conclusion, for some people the testing of pharmaceutical drugs on animals is entirely justified and appropriate. Although I would agree with this to an extent and would argue that human lives are more important than animals, I also think that the alternatives to animal testing need to be further developed.