Not even 24 hours have passed since the Government's announcement of a federal flood levy, and the "Heartless Bastard" debate is well under way.

The anti-levy team reckons Julia Gillard and Wayne Swan are Heartless Bastards for whacking generous Australians, volunteers, battlers and so on with a tax that will - combined with really, really expensive bananas - bring household budgets to a state of near-collapse.

The pro-levy team, on the other hand, thinks that anyone whingeing about the impost is a Heartless Bastard who doesn't care about helping flood victims.

The lines thus drawn, I imagine we'll now have a mutually satisfying all-in screaming match until 1) the banks put up interest rates out of cycle again, 2) everybody notices how much petrol prices are going up, or 3) Gordon Ramsay says something horrible about an Australian.

There is a reason, though, why this levy has been more divisive than some of its predecessors (the federal gun buy-back levy, the proposed East Timor levy, or the levies aiding Ansett employees or dairy farmers).

This levy was announced after an extraordinary bout of unforced national generosity.

The psychological effect, therefore, of a compulsory additional levy, is twofold.

First, you get the "ouch" factor of knowing that your tax return is going to carry some extra weight in the red column.

As "ouch" factors go, it should be said this one is not especially huge or crippling, but it's there, for many Australians.

But the second factor is more nebulous, and I reckon it accounts for the pockets of anger about the levy.

It's to do with the feeling that unforced generosity imparts to the giver, a sort of kindness endorphin; personal satisfaction, the feeling of well-being associated with helping someone else, and the sneaking sense that perhaps one is not such a bad person after all.

When a compulsory contribution is demanded on top of the voluntary one, petty resentments can crowd to the fore.

"What? But I already made a really, REALLY big donation! That's not fair! I'm being punished for my own generosity!" and so on.

And like that, the good feeling has evaporated, leaving some givers doubly aggrieved; the extra financial burden of the second contribution, plus the loss of the warm fuzzy feelings associated with the first.

I'm not making a point either way about the levy here; I'm just trying to understand the reactions of people who are responding angrily to it.

What do you think?

Annabel Crabb is ABC Online's chief political writer.