Robinson criticizes liberals for believing that one can legislate free speech (influence) in a society that creates gross inequality in the distribution of money. Money is influence.
Capitalism creates classes by essentially dividing people into "owners" of productive property and workers who work in their property for wages controlled by the owners. The owners will always come of better in this system because of their control of wages. Over time this control has inevitably resulted in what we see today: a small segment of the population who are rich and vast number of people who tend to be poor and powerless (without influence). Thus, you can have many laws regulating the use of money to influence the political process, but money (influence) will always be used by capitalists to dominate society. Capitalists will always find ways to work around any laws or regulations that tend to restrict their influence. This last conclusion has been demonstrated throughout the history of capitalist societies.
...money not only buys political power, it is political power. Its possession confers godlike capability, and its deprivation creates servitude. With money one can manipulate public taste, ruin one’s enemies, and build, destroy, and conquer.