It will work now because of technology. Last time doesn't work because not enough of tech.
But the other factor is we must get rid of useless eaters, practice eugenics.
Sterilize people who have more than 2 children and remove unproductive humans from the gene pool.
Population must be cut down to manageable levels.
And finally, complete destruction of all major religions.
Religion is the cancer to the progress of humanity. Destroy it and all those who spread it.

Yup. 

So back to the original question, if free market not good for world economy, then what is good?

If anyone can name an economic system that is not based on the pursuit of profit (a.k.a. greed) then that's the answer.

If greed is not bad, then why even bother to regulate it?

You can start from faceless's post @4:05pm.

I can think of market manipulation tricks such as short selling and hoarding in order to create artificial shortage to jack up prices. The regulators.. a jail sentence if convicted?

How about the simple logic that ponzi schemes don't work ?
Fiat money, is ponzi.
How can you print money out of thin air and lend, then expect to be paid back in real interests as well!?!!
Where's the interests going to come from ?!!!!
From real stuff, you dig from the ground, or foreign exchange, where others dig from their ground.
Do you see how wealth is transferred from the bottom barrel peasants to those at the top?!
Mainly the oligarch banksters.
It is a form of slavery! Most cannot see through it because they're bamboozled and blinded by materialism.
They don't realized someone's gotta pay for it for them to enjoy what they got. That's why the bottom barrel losers are the poor, the starving, whose land are being raped and they're left to fend for themselves, regardless of what country.
The ponzi/pyramid scheme is illegal only because the entire financial world and governments are using this pyramid scheme!

Of course, we all know what happens to pyramid/ponzi schemes eventually, especially in the financial world. They will collapse under their own unsustainable weight/lifestyle and debt.
This is the foundation of our world, the pyramid binary universe/tree scheme of all things!

Population control and eugenics is the answer.
Sterilize people who insist on having more than 2 children and those who don't have the brains should not reproduce.
We start with the religious nutjobs.
'Go Forth and Multiply' type of people.
This way we reduce uncontrolled demand/consumption.
Instead of waiting for them to overpopulate before we resort to either soft or hard kill to take them out.
Better to not have these humans born than to have to kill them later to sustain the future of the entire human race.