There is empirical evidence showing that ethical investments provide returns as good as normal investments.
Consider the following:
- “Since its inception in 1999, through 2013 the MSCI KLD 400 Social Index has had an average annual return of 10.24%, while the MSCI USA Index (its peer, non-social index) has had a slightly lower average annual return of 9.79%. Numerous academic studies, as well as analyses by Morningstar and Forbes, have concluded that it is “surprisingly difficult to prove that social screens make any significant long-term difference to investment returns.” (Morningstar, “Social Responsibility and Fund Performance,” March 12, 2012) 
- “Online retailer Zappos started from nothing in 1999 and was sold 10 years later for $1.2 billion, while consistently being listed as one of the world’s most ethical companies.”