Experimenters can justify the use of deception because

This is justified on the basis that for an experiment to work the deception is necessary a must. The experimenters sometimes need to deceive their test groups in order to gain more objective results and also to eliminate the possibility of the subjects knowledge of the experiment interfere with the results. The example of this is to prevent the placebo effect. Sometimes even the administrators of the experiment are not aware of the which is the medicine and what the placebo and this is called double blind experiment.