I have seen videos where he explains: insurance pays for the medicine, not individuals, and people who can't afford/have insurance gets them freely from government programs/their company programs.
And who pays for insurance? (Hint: It's individuals) Shkreli is right in that by raising the prices he wasn't really gouging the sick for thousands and thousands of dollars, he was gouging all of us with insurance for some fraction of a penny. It's still wrong.
Also drugs are not the largest part of insurances pay for.
Also, I'd suggest focusing on the wider picture. Price gouging on a single drug may have a minimal impact, but there have been numerous cases of drug companies artificially hiking prices of their products, which does make a substantial difference. There are numerous studies into this if you're interested.