It can't be used to defend all forms of experimentation since there are some forms of suffering that are probably impossible to justify even if the benefits are exceptionally valuable to humanity.
The proposed directive covers all live non-human vertebrate animals intended for experiments plus certain other species likely to experience pain, and also animals specifically bred so that their organs or tissue can be used in scientific procedures.
The Top 3 Ways Animal Experiments Hurt Humans | HuffPost
...whenever experimenters claim that their experiments are important enough to justify the use of animals, we should ask them whether they would be prepared to use a brain-damaged human being at a similar mental level to the animals they are planning to use.
Obama greenlights human-animal 'hybrid' monsters - WND
Whatever benefits animal experimentation is thought to hold in store for us, those very same benefits could be obtained through experimenting on humans instead of animals. Indeed, given that problems exist because scientists must extrapolate from animal models to humans, one might think there are good scientific reasons for preferring human subjects.
Arsenic-based Animal Drugs and Poultry
The issue of animal experiments is straightforward if we accept that animals have rights: if an experiment violates the rights of an animal, then it is morally wrong, because it is wrong to violate rights.
The welfare of animals used in research is very important
Moreover, a great deal of animal experimentation has been misleading and resulted in either withholding of drugs, sometimes for years, that were subsequently found to be highly beneficial to humans, or to the release and use of drugs that, though harmless to animals, have actually contributed to human suffering and death.
Fasting diet 'regenerates diabetic pancreas' - BBC News
. A brave and truly historic exposé of pig-to-primate organ transplant experiments in the UK, followed by a monumental legal victory over biotech company Imutran and their parent corporation Novartis, on public interest grounds. Uncaged won the right to place thousands of confidential documents into the public domain, giving an unprecedented insight into the harrowing reality of animal experiments and collusion between researchers and government to avoid animal welfare regulations.
Scientists are only human, and some humans are just plain crazy
Uncaged was uniquely holistic. We operated at every level, from grassroots protests to lobbying Parliament, through to participation in academic discourse. We contributed to numerous Government consultation exercises on animal experimentation matters and gave evidence to their enquiries. Our analysis appeared in journals and was quoted by researchers. National and international media covered our groundbreaking work.
In the animal experiment context, if the experiment takes place, the experimenter will carry out actions that harm the animals involved.
The possible existence of immune surveillance mechanisms that prevent the development of cancer is supported by the finding that immunodeficient individuals and patients undergoing long-term treatment with immunosuppressive drugs are at greater risk for cancer than the general population. Experimental evidence that directly links immune mechanisms to the defense against cancer comes from classic experiments in which immunized mice rejected chemically induced syngeneic tumors.2 Naive syngeneic mice (i.e., mice not previously exposed to tumor) were protected against tumor growth by immunization with killed tumor cells administered before challenge with viable tumor cells [see Figure 1]. The specificity of this immune response was demonstrated by the lack of protective effect of prior immunization with killed cells from an unrelated tumor. The important role of lymphoid cells in this immune response was demonstrated by the protective effect of spleen cells from a tumor-bearing mouse administered to a naive host (adoptive transfer of immune cells) before tumor challenge with live tumor cells. In these experiments, the cyto-toxic T cell population (CD8+ T cells) within the spleens of tumor-bearing mice demonstrated unique protective activity upon transfer. Transfer of helper T cells (CD4+ T cells), B cells, or serum-derived antibodies did not confer protection in this model. The results of these classic experiments, in which syn-geneic tumors could be rejected in naive hosts receiving prior immunization or by adoptive transfer of immune cells, support the existence of tumor-associated antigens in animal models and form the basis of much of the experimental work in human tumor immunology.