Shkreli's main sin is choosing a drug that is primarily used by a specific protected class. It treats parasitic infections that normally don't take hold in people with healthy immune response. Daraprim's customer list is something like 92% AIDS patients, and 8% immuno-compromised for other reasons.
Shkreli did something that happens all the time, and we don't bat an eye. But you don't do it to protected classes without a mob response.