Lindsey Tanner throws a hissy fit because our political system isn't locked between two major parties like in the US

Resident ALP whiner Tanner doesn't like the Greens. Last election, he ran a few Fieldingesque home movies attacking the Greens and this election, apparently stripped of his video playthings, has been forced to go for a more low-budget response: the opinion page.

Green voters typically either have or are getting a tertiary education. Support is concentrated among tertiary disciplines focused on more than making money. Their viewpoint is increasingly at odds with that of Labor voters who aren't tertiary educated. On issues like asylum seekers, forests and civil liberties, differences can be stark. The Greens seek to exploit them.

No, the Greens aren't 'exploiting' any factions. We're just representing environmentalism and human rights. By adopting Howard's policies, the ALP has abandoned its left faction. That more lefties and not just environmentalists are supporting the Greens is your doing, not ours.

Whatever Labor does, it is never good enough for the Greens. Even when we're repealing WorkChoices, apologising to indigenous Australians, or tackling climate change, they attack Labor for their own cynical purposes. If the Greens had voted with Labor, the Senate would have passed the climate change legislation.

No, that wouldn't have happened at all. You're conveniently forgetting Steve "Thank for the ALP Right is so cynical in its preferences" Fielding. The guy who your party got elected in 2004, and has adopted the Abbott policy of flat out denialism. Even if the Greens had supported your total sellout of a policy, which had been so watered down by working with Turnbull it was in every way worse than useless, the bill would've never gotten past Fielding. That you couldn't pass it is your doing, not ours.

We now have no legislation at all. The Greens' political posturing took precedence over action. Their policy would have no chance of passing the Senate, even if Labor supported it.

Of course not. We don't yet have the balance of power. This election will (hopefully) change that. And stop with this 'obstructionist' meme you're running. The Greens didn't support it because the bill would've locked in failure. Australia would have unable to reduce its emissions by any more than a pitiful amount. The Greens were right in opposing it, and were supported by the overwhelming majority of greens.

The Greens are not some benign group loosely allied with Labor. They're not a middle-ground party. They're not idealistic activists changing the world. They're just another political party, no less cynical or manipulative than the others.

No, we are less manipulative and cynical. That's seen every election. The ALP routinely lies about, and demonises the Greens in the constant hope that throwing every smear it has will keep its dwindling progressive supporters on board. The Greens advocate three simple things: public services, civil rights and liberties, and protecting the environment. Those three objectives are far less extreme than you'd like to think.

It might seem like a good idea to support those who yell the loudest, but it's unlikely to produce good outcomes. Labor is the only worthwhile option for achieving progressive change through parliamentary politics. It might be a bit piecemeal and gradual, but it beats the hell out of doing nothing.

No, the ALP doesn't represent "progressive change." It abandoned progressive values when it sought to out-Howard Howard. The ALP support the internet filter, the draconian anti-terror laws, an inhumane refugee policy, tax cuts over public services, the forestry industry over forests, keeping gays from expressing their love, and I would imagine a whole host of other anti-progressive policies. Because Labor is a 'big tent' party, as a progressive voter I have no idea if you will represent my left-libertarian views in parliament (actually, I do have an idea. It's a big fat 'no, you'll keep treating me as a chump while remaining a fundamentally rightwing party'). But when I vote for the Greens, I actually know what I'm voting for. I know that they will represent my views in parliament (not precisely, of course, but they're by far the closest to my beliefs).

If you're so afraid of the Greens taking your precious votes because people are beginning to realise that the Greens actually represent the mainstream left, then you can start by actively trying to represent the mainstream left yourself. You could start by lobbying the ALP to legalise same-sex marriage. Then, you could adopt Latham's Tasmanian forestry policies and support treated pine plantations rather than logging and wood-chipping native forests.

Above all else, if you want lefties to keep voting for you, than you have to actually represent them in parliament. Instead, you've just taken the easy route-pushing further to the right, whilst assuming lefties are too brain dead to recognise just how Liberal you've become. But this isn't America. Australia actually has a proper, representative democracy where minority views can be expressed. I know just how much you hate that.