The donors and their lobbyists claim their contributions are some form of civic philanthropy: they're just helping finance election campaigns to ensure a vigorous contest of ideas and a healthy democracy.

And the politicians insist the money comes with no strings attached: it does not buy access or influence or favours or votes. But it does save taxpayers the cost of financing those election campaigns themselves.

Now the facade is slipping.

This past week the Minerals Council of Australia - in a Senate submission - admitted it makes donations to gain access to politicians.

Well, of course it does. We all knew that. It's a lobby group that works for some of the country's biggest companies.

Nonetheless, it was confronting - and maybe also a little refreshing - to hear them say it. Other prominent companies and groups sought to maintain the "supporting democracy" fiction in their submissions.

So what sparked this sudden candour?

Was it a deliberate decision to be more honest? A mistake that snuck into print? Or has the culture whereby the wealthy buy political access become so normalised that the players in this game now see it as entirely uncontroversial?

It's reminiscent of comments made by Finance Minister Mathias Cormann last month as the government announced its long-overdue crackdown on foreign donations: "Only Australians, Australian businesses, Australian organisations should be able to influence Australian elections via political donations."

Of course Australians - be they companies, unions, activists, charities or individuals - can seek to influence politics. That's their democratic right.

But there's a difference between contributing to the marketplace of ideas and using buckets of money to directly line the coffers of the political parties in a bid to gain access and influence over policy.

By Cormann's own admission, donations bring influence. Logic follows then that the bigger the donation, the bigger the influence.

That's not to say donations always translate into policy changes that benefit the donor, or lead to lucrative government contracts.

But private money now so thoroughly undermines public trust in politics it is corroding the very foundations of our democracy.

Donations have become synonymous in the Australian mind with privileged access, shady deals and in some cases real corruption.

Even when governments make the right policy decisions for all the right reasons, many people now assume there are powerful vested interests hidden from view, holding the purse-strings and pulling the puppet-strings.

The government has made a start on donations reform. Labor has promised to go further. But we may well have reached the point where only full public funding of election campaigns can restore trust in the system.

Like the government's new independent parliamentary expenses authority - or a potential federal anti-corruption body - publicly funded campaigns would be another burden on long-suffering taxpayers.

But if we care about the integrity of our democracy we need to invest in it.

Adam Gartrell is a political correspondent.