The Congress Documents state the following: "In the same way, the stock markets, too, instead of losing influence, contrary to conclusions of Comrade Lenin, have become even more influential in the form of legal giant casinos, becoming means to exploit the labours of billions of people." (p. 25)
This is another case of lack of comprehension of Lenin, of arbitrarily interpreting his text, or being amazingly ignorant of the content of his writings. Based on what is being said on stock markets in Lenin's book on Imperialism, in the section where the bourgeois economists' interpretations are reviewed, to come up with such a claim is plain distortion, as the MKP does. If this were not to a deliberate distortion, the MKP would have ignored what Lenin had written in 1919, a few years after he wrote his book Imperialism:
"What, it can be asked, is altered in this respect when capitalism gives way to imperialism, i.e., when pro-monopoly capitalism is replaced by monopoly capitalism? Only that the power of the stock exchange increases. For finance capital is industrial capital at its highest, monopoly level which has merged with banking capital. The big banks merge with and absorb the stock exchange. (The literature on imperialism speaks of the declining role of the stock exchange, but only in the sense that every giant bank is itself virtually a stock exchange.)" (Lenin, A Caricature of Marxism and Imperialist Economism, p. 54-55) [https://www.marxists.org/archive/lenin/works/1916/carimarx/3.htm]
How could one misinterpret such a clear explanation on the increase of stock markets' power? There is more. As if to directly refute the MKP, on July 11, 1919, Lenin says the following: "The power of capital is everything. The stock exchange is everything." (Lenin, Marx, Engels, Marxism, p. 303) [https://www.marxists.org/archive/lenin/works/1919/jul/11.htm]
It is a fact that there is a difference between the role of the stock market at the beginning of the free competition capitalism and at its later stage and finally its role at the monopoly stage.
While preparing Marx's Capital for publication, Engels, in his addendum to the Volume III of Capital, underlines that the stock market has gained a lot more importance since Marx wrote the book:
"The position of the stock exchange in capitalist production in general is clear from Vol. 3rd, Part 5, especially Chapter [27]. But since 1865, when the book was written, a change has taken place which today assigns a considerably increased and constantly growing role to the stock exchange, and which, as it develops, tends to concentrate all production, industrial as well as agricultural, and all commerce, the means of communication as well as the functions of exchange, in the hands of stock exchange operators, so that the stock exchange becomes the most prominent representative of capitalist production itself." (Capital, Volume Three, p. 794) [http://www.marxists.org/archive/marx/works/download/pdf/Capital-Volume-3rd .pdf]
Yes, today these developments in the stock exchange have reached gigantic proportions, making it the heart of deterioration as well as steering centre of the economy. It is now pretty much impossible to come up with an opinion on any economic and financial problem without having followed the stock exchange.
Stock market is an unprecedented type of casino, where stocks, bonds, and derivative financial assets, representing goods and services, as the bourgeois media often mentions, are exchanged at great speed and quantities; it is a casino from where stems out the "imaginary money wealth." (Karl Marx, Capital 3rd , Section 30, Money-Capital and Real Capital I, p. 424) At stock exchange the repossession and movement of property rights take place via bunch of valuable papers and hence it becomes an arena for endless game of gambling and fraud.
Moreover, wealth that occurs here is a virtual one, assuming a body as an imaginary capital.
It is because Lenin had seen this fact and the extent to which the subsequent developments had reached that he had said, "stock exchange is everything."