The state does not have any money, it takes money in taxes we all agreed on to use it in fair way, and that is not to use the power of the state to buy up your livelihood and give that to a party member, that would be unfair.
For any other value of "we all agreed" then it sounds like you're arguing that the vast majority of government expenditures are unjustified. That seems like a much more expansive claim than what you're trying to make.
Why should it be okay for the state to use tax money to purchase a tank or a mile of road but not to purchase a share of stock?
State can of course buy stock. State owned companies can work just fine.
But there is a difference in intent. Intent here was union controlled ownership of all major companies. Creator of idea explicitly quoted Marx.
It think also we got bit sidetracked in this discussion with the word buy that I misused, it was not buying at the stock market, it was "buying" with legislation, exchanging profits for stock.