Adding May didn't detract from the debate. Today, with Ford's Tories vowing to dismantle cap and trade, and block any form of carbon pricing to reduce global warming, excluding the Greens from the discussion will deprive voters of an important voice.

Then as now, the networks argued against giving the Greens a voice because they didn't yet have a seat. But this is putting the cart — or in this case, the seat — before the horse. How is a political movement supposed to make headway without having a way to be heard?

Then as now, the networks argued that the Greens have no prospect of winning power, so it's pointless to distract voters with also-rans. This is another Green party red herring, for the television networks had previously invited the Western-based Reform party and the Bloc Québécois to participate, despite their narrow regional power bases.

May ultimately won a federal seat, as did her fellow Greens in B.C., N.B. and P.E.I., after debate appearances — proof that (televised) appearances matter. Adding a fourth leader to the fray in Ontario would not render this month's debates any more unwieldy than the five-person debates of past federal elections.

The Greens have consistently run candidates in every riding in Ontario, and attracted significant voter support in past elections, ranging as high as 8 per cent. That's far more than any fringe party.

But there is one new factor that changes the calculation: Like the three biggest parties, the Greens receive a per-vote public subsidy, as part of the campaign finance reforms brought in before the election to curb the influence of corporate and union donors.

Even if the Greens don't win power, and even if they don't win a seat this time, it is manifestly unfair to deprive them of the chance to attract voter support — and the financing that follows — during a debate. It is also anti-democratic to deny voters the chance to scrutinize the performance of any publicly subsidized party.

There is still time for CityNews to do the right thing and open up Monday's debate to Ontario's fourth major party. And there is more than enough time for the networks to revisit their scheduled May 27 debate to be aired by public broadcasters CBC and TVO, along with Global, CTV, CHCH and CPAC.

For too long, the so-called network consortium has consorted behind closed doors to arrange ad hoc debates to its own tastes, instead of displaying transparency and fidelity to democracy. Ontarians deserve an open discussion about election debates, so that voters are free to make their own choices — without TV networks deciding on their behalf who is and isn't worth considering.

Martin Regg Cohn is a columnist based in Toronto covering Ontario politics. Follow him on Twitter: @reggcohn