One school of thought about the effectiveness of subliminal advertising is that effectiveness is only partial because brains can only assimilate large concepts of subliminal messages but cannot assimilate inner details of the concepts. Yet, according to this school of thought even though only large concepts are absorbed, the main intent of the message is nonetheless successfully delivered.
The other school of thought about the effectiveness of subliminal advertising is that regardless of the lack of conscious realization, details of messages are absorbed along with the large concept. This school of thought relies on research studies that show that people with brain impairments or vision impairments of one sort or another who believe that they do not perceive specific bits of information they are exposed to nonetheless give later responses that draw upon the information they were exposed to but didn't consciously perceive. This shows that the brain has one or more mechanisms for acquiring knowledge and drawing upon that knowledge that exist and function below our level of consciousness.
This is an overview of the two dominant schools of thought about the effectiveness of subliminal advertising. When deciding on your position regarding the effectiveness of subliminal advertising, it is a fair assertion to claim that the side with the most research is the one that presents the more viable option. A deeper investigation than is possible in this brief format is required before determining which school of thought has the strongest empirical basis (research-backed basis).
If your task is to decide and explain your position regarding the ethics of subliminal advertising, one of the most cogent points in determining a position on its ethicality is the fact that subliminal advertising subjects people to messages against their will, without their consent, and without their knowledge. To the general public, this kind of invasive intrusion into the ultimate privacy, the privacy of thought, is considered unethical in the extreme; it is also considered domineering, manipulative, obtrusive and brutal. Thus, in deciding your position on the ethics of subliminal advertising, you will want to evaluate these charges against subliminal messaging in advertising.