The allegations are two-sided in ASIC's latest legal action, its third against a major Australian bank, for "unconscionable conduct and market manipulation in relation to National Australia Bank's involvement in setting the bank bill swap reference rate."NAB becomes the corporate regulator's third target, following ANZ and Westpac.Commonwealth Bank is the missing major, still to emerge as the target of any corresponding legal action.The language, in the first paragraph of ASIC's originating process for the civil action, zeroes in on a fundamental ambiguity in the regulator's zeal to snare a major Australian bank for borderline criminal conduct.The claimed insult to Australian society from the three banks' actions is that the enterprising engagement of each bank with their peers in this capital markets niche was "likely to mislead the public as to the characteristics and suitability for their purposes" of BBSW.That's it.There is no florid language on business borrowers, to whom BBSW is most relevant, being ripped off.The language is that of Labor leader Bill Shorten."How many more people need to suffer and get ripped off before [Prime Minister Malcolm] Turnbull stops covering up for the banks?" Shorten said yesterdayThis aspect of the debate must be ripe for reset.There is no rip off, other than what the Big Four banks are doing to each other, amid the antics of the rate set on 30 day, 60 day and 90 day money.Arbitrage is the path to generating gains and returns from the ton of bank capital allotted to a bank's treasury. Four banks, each staffed with talent brimming with confidence and guided to take the plunge each day to make a measurable profit for the company.That profit and loss is one monitored pretty acutely on a bank trading floor, an aspect of industry culture which deserves appreciation.A degree of urgency on the part of the workforce might be another feature to consider. The accepted practice in the industry - to jettison costs and attain stretch profit targets - is a monumental dynamic in treasury.Mix in cocksure artisans, only too willing to outsmart the others, and off they go.It's a flipping financial market, people.There'd be no trading in any commodity beyond barter if humanity's risk takers didn't chime in with all the entrepreneurship society beckons from its brightest. In banking, we're talking about a cohort of hundreds and thousands of talented workers, a true industry pillar.These people are doing what they're paid to do in a capital market. Inspired by ten thousand predecessors to value risk taking, this mob strive for returns governed by intellect more than chance.The management team at each bank, c'mon, they're chasing down superstars on the trading floor, a team often recruited from ruling class schools to populate the bank with reliable operators.A stack of bank operatives in rates trading, FX and many disciplines have sole or team responsibility for a chunk of bank capital, getting the bank funded in the cash market being an indispensable start to the day.There's an eighteenth century ethic in Australian banking, a quaint reminder