Stephen Foley: Wall Street firms are leading the way when it comes to workplace diversity

US Outlook: 'I'm Lloyd Blankfein, chairman and CEO of Goldman Sachs, and I support marriage equality.'

Much ink has been spilled since the vampire squid boss came out for gay marriage in a video for the Human Rights Campaign lobby group this week, but those who found Mr Blankfein a startling choice of public advocate have not been paying attention to what has been happening on Wall Street for the past decade.

Apart from perhaps the big law firms, investment banking tends to score highest of any industry on those checklists of good diversity policies. Not only do they have the anti-discrimination ethics codes and equal opportunities recruiting rules that are de rigueur in the modern workplace, but where the tax code favours married couples, banks are now topping up the pay of gay employees unable to marry their partner. If anything, the ability to boast about fairness has become one of the many pissing contests between big banks.

There is much more to be done, not least to stamp out the vestiges of frat house culture on the trading floors of banks. For all Wall Street's commitment to diversity, stories abound of new recruits getting hazed – cruel practical jokes, teases and tricks that used to be explained away as team bonding and tests of loyalty, but which are actually just workplace bullying. It is not Wall Street's addiction to booze and strippers that makes life hard for gay and lesbian employees; it is fear of the casual workplace cruelty that can be meted out to anyone who is different.

Usually the reality of coming out on Wall Street is better than people expect, and some powerful academic work shows that employees who hide their sexuality are more likely to feel frustrated at work and stalled in their career. Banks benefit from nurturing the "employee resource groups" set up by gay and lesbian employees, which serve as informal networks and provide role models, even mentors. Increasingly, these networks are not about protecting oneself from discrimination; they are about getting ahead. A gay banker can be as careerist as the next person.

The next front is to equalise treatment for bi-national gay couples, for whom discrimination in immigration laws can be a real drag on a career. Banks have to come up with creative ways to advance gay and lesbian employees who may not be able to take a promotion abroad (or into the US) because their partner could not get the visa that would be available to a married person.

This is a pain as much for the multinational bank as it is for individuals involved, since it adds a consideration beyond simply who is best for what job.

But the truth is, big corporations are bumping up against the limits of what they can do on their own. Lobbyists for a proposed Uniting American Families Act hope to recruit Wall Street donors to promote immigration equality, but nothing would be more effective than allowing gay couples to get married.

That is why you see banks throwing their financial and public relations weight into lobbying for changes to the law, as Mr Blankfein did this week. And why you will see more of it.