In an attempt to preclude accusations of snarkiness, I'll refrain here from asking why the higher professions have found it necessary to develop and publish elaborate canons of moral and behavioral ethics for mandatory compliance by members while plying their various trades. I'll simply note that the productive professions have done just that, while the political profession-ideologues and pragmatists, active politicians and passive commentators-has not.
Thus, members of the California bar are required not to withhold evidence which, if released to the opposition, might damage their own chances for a courtroom victory. I'd guess that the rule was put in place because "winning trumps everything" barristers might otherwise do just that sort of withholding and prior reliance on idealistic notions of conscience hadn't worked without a printed rule. This now appears in the California Code of Judicial Ethics: Canon 3D. It identifies seven categories of egregious lawyer conduct.
For example, item 4 of the California canon specifically proscribes "...Willful... withholding... exculpatory evidence... " Presumably, if item 4 weren't there, lawyers would do just that. Now, with rare exceptions, they don't. Having chosen not to adopt the written code, the political profession usually does.
Here's an example-
Drawing on a recent state-by-state income/wealth versus taxation study by the Washington-based Institute on Taxation and Economic Policy, the Vermont-based Public Assets Institute published a news release last week with this ITEP quote: "...The Vermont tax system already falls most heavily on the very poorest families in the state."
You can find this 130-page study-with its multi-color bar graphs showing percentage-of-income tax levels for all income quintiles for all states-on the ITEP website.
Vermont is shown with the bottom income quintile paying 8.2 percent of income and the fourth quintile (middle-income) category from $54 to $85K paying 9.2 percent (an ITEP fact about distribution of tax burden not deemed mentionable or reportable by PAI) while the top quintile pays an average 7.7 percent, lower than the bottom quintile, hence the PAI equality-based-outcome-seeking angst.