Economic regulations often help the biggest companies by keeping out new entrants and imposing costs that fall disproportionately on the little guys.
The Democrats' 2010 Dodd-Frank financial regulation bill included a provision known as the Volcker Rule, which is supposed to stop banks (that is, institutions backed explicitly and implicitly with federal guarantees) from engaging in proprietary trading (that is, investing their own money for their own profit, rather than investing clients' money for clients' profits).
This rule necessarily has exemptions, and I've argued that the big guys would find ways through these exemptions. We've already seen how the rule is disproportionately crushing small guys.
As the final rule has come down in recent weeks, there's no doubt it will curtail profitable activities by big banks. But one analyst has an interesting argument for why the rule helps investors in Goldman Sachs:
I believe the markets have already factored in negatives associated with the Volcker rule. More importantly, GS has had time to adjust its business for a considerable amount of time prior to implementation. This leads me to why I believe the Volcker rule may actually be a bullish catalyst for GS. ...
A decreasing reliance on proprietary trading may very well lead to lower profits over the short term. However, the decreasing reliance on proprietary trading, will in my opinion, lead to a significant increase in the premium investors are willing to pay for GS earnings stream.