At a restaurant you trade money against a good meal. Wealth just got created.
You valued your money less than the meal, and the cook valued the meal less than the money. The sum of the difference of valuation is wealth.
Not all trade is equal. Most of the time there is a power relationship where the strong exploits the weak.
An example is sweatshops. People who need jobs are willing to allow themselves to be exploited because they need money. This was common in 19th/ early 20th century before existence of labor unions
Don't get me wrong, I don't deny the good of labor unions. They did lot of good and they are not against libertarian principles.
This is entirely normal that labor can collaborate together to put some pressure on industrialist. Industrialist does the same under cover.
What I deny is when the state subsides either them or when it enforces policies for the sake of one or the other.
But before labor unions, the person that worked in a sweatshop, decided it on his own free will that it was better for him than any alternative.
He valued money more than his labor. And the workshop valued his labor less than money.
Both worked together without coercion. And among all alternative, the worker chose with his free will the conditions.
The worker could go back in country side if it was so hard in the city.
The worker could learn to use his mind instead of his body, he could change city, but he did not.
Industrialist offered jobs that workers could not find in countries.
Also with the concentration of labor came urbanization and the abundance of economical activities (and thus goods), not found in country.
New villages and cities could be founded thanks to the need of labor of factories.
You can't say that both, the worker and industrialist destructed wealth by collaborating together. They both gained.
This is normal that both wanted to get more for their own work/money. But they were trading freely, and both of them needed the other.
Libertarians are not against people from collaborating together into a social structure so all members inside can personally benefit from the association.
As long as the members of this association have the right to disassociate freely, don't get subsidy of government, and don't use its coercion power for their own goal, this is beneficial. (These conditions are sadly not respected in France anymore)
One quote from Atlas Shrugged, from Francisco D'Antonia :
"But you say that money is made by the strong at the expense of the weak?
What strength do you mean?
It is not the strength of guns or muscles.
Wealth is the product of man's capacity to think.
Is money made by the man who invents a motor at the expense of those who did not invent it?
Is money made by the intelligent at the expense of the fools?
By the able at the expense of the incompetent? By the ambitious at the expense of the lazy?
...
Have you ever looked for the root of production?
Take a look at an electric generator and dare tell yourself that it was created by the muscular effort of unthinking brutes.
Try to grow a seed of wheat without the knowledge left to you by men who had to discover it for the first time.
Try to obtain your food by means of nothing but physical motions – and you'll learn that man's mind is the root of all the goods produced and of all the wealth that has ever existed on earth.