My mother is entirely averse to putting any money into the stock market. Her stated main concern is that she doesn't want to be "supporting" companies that are engaged in moral wrongdoing.
It's my understanding though, that when you buy/sell stock in the market, you're doing so second-hand-- i.e., to some other individual and no money ends up going to the company whose stock is being traded. That it's akin to buying something in a thrift store or on craigslist, where no portion of the money that changes hands goes back to the original manufacturer.
The exception to this would be an IPO, of course. (Are there other exceptions?) But does an index fund like VTSAX include purchases of IPOs?