But changing a policy, introducing a tax or making a service more accessible introduces consequences elsewhere that can't be brushed aside with sweeping rhetoric.

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Labor has been unable or unwilling to talk about the broader costs of its approach in a string of areas, not just taxation.

At his press conference in the South Australian marginal seat of Boothby, Shorten didn't want to deal with the potential economic cost of Labor's plan to reduce carbon emissions.

Yes, there is a cost from not acting - of that there is no doubt. And the Coalition doesn't want to talk about that.

But from electric vehicles on our highways to the costs facing the energy sector as it transitions to a low-carbon future, Labor has explained how the policy will work but failed to address its economic consequences.

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The Coalition, incoherent in environment policy for the past decade, is set to unveil its own "modelling" in a bid to define Labor's position. Labor risks allowing the government to set the terms of this debate unless it starts answering reasonable questions on its broad plans.

The way negative gearing intersected with the capital gains tax concessions introduced by Peter Costello in the late 1990s was a key factor in the explosion in house prices from that point.

Labor's plan to undo that element will have effects it has not yet confronted. It's more focused on the budget bottom line, which will swell under its tax agenda.

However, it's important not to confuse the budget with the economy.

Labor under Shorten has moved further than any opposition in a generation in terms of being upfront about its policy prescription.

But with that policy there needs to be an honest explanation of more than just numbers in the budget.