I understand your concern. Yes, the drug companies do use "social phobia" to create additional market for their drugs, as they did in India for Hepatitis B. But the decease exist and it IS dangerous. Only they created a huge market to sell the drugs at one point of time.
But I've never heard of the companies to market drugs for non-existent deceases.
In counter of your argument I would request you to go through the following links. They are from medical community.
http://www.medicinenet.com/human_immunodeficiency_virus_hiv_aids/article.htm#
http://www.avert.org/hiv.htm
If you are unfortunate to visit a few African countries, you may not be so much skeptical about the existence of AIDS which is caused by HIV virus.