It seems to me that we have to try to clarify how democratic workers control can be exercised over the economy. The key question is how is the surplus, which is produced by the whole society (globally) to be allocated? At a given point in time, how much resources are to be devoted to, say, building new factories that make construction equipment, or tractors, or cars or refridegerators or clothing? How much construction for new housing or for schools or for hospitals?
If what Julien and DC are proposing is that an individual factory be collectively owned by the workers of that factory, then the allocation of surplus will be made by the market, and you will still have capitalism. Worker-owned factories will only be able to expand production by making a profit, selling at more than their costs. Each worker-owned collective will be operating as a capitalist, subject the same economic laws that Luxemburg describes. Maybe this is not what either of you are talking about, but if not, what do you mean?
I think the questions of ownership and democratic control have to be separated. In Yugoslavia, factories were owned by worker-collectives, but there was no democratic control.
To have a democratically-run economy, society needs to be able to allocate surplus freely, so you can’t have ownership at a local level. You need state ownership because that way you do not need for any unit to be producing a profit. A state can allocate resources that are produced by the entire society.
But as Marx pointed out after the Paris Commune, you can not have a bureaucratic state. Like the commune, or the strike committees that arise in mass strikes, you need decisions made by workers delegates, who can be mandated and revoked. Exactly how this can be done in large countries, where you would inevitably need several layers of delegates, how decisions are to be made at national and local levels and many other questions are not easy and it would be utopian to try to work them out in advance. But the basic point is that you do need a democratic state to make economic decisions and it has to own the major means of production.
This question has very practical implications for the workers movement. The nationalization of the steel industry in Venezuela happened because the workers in the steel industry forced Chavez to do it. They were involved in a long-running strike, where the governor of the state in Venezuela was using the National Guard against the strikers. But by mobilizing the community behind their demands for nationalization, the workers war able to win. I think they were right to demand nationalization. We would be wrong to oppose it. But now, the battle will really begin as to how the steel industry is run. Will it be run by delegates elected by the workers or will it be run by bureaucrats reporting to Chavez?