This is a disingenuous argument by your friends that betrays a mechanical understanding of the world. Yes "owning" financial instruments does 'legally' give you some measure of ownership of a company, but functionally you really have no control over the shares of the stock. This is not an accident, as the law is was written with the intention of ensuring that these stockholders would be silent partners. Much of the post Great society retirement scams have been built around primarily not giving people vehicles to save for retirement but giving free capital to companies, the mechanisms of which are largely obscured by the system. For example if your company opens a 401k for you when you start working there, unless you take the time to go through the headache of decoding the financialease and mapping out their purposefully labyrinthine website, your retirement funds will almost always be allocated in a manner that helps the company; in some cases it will be entirely invested in the company itself. This is one reason companies dont mind giving their employees investment matching as it is basically a free bump to their stock prices.

Additionally even if you ignore these sorts of shenanigans, most people dont actually manage the funds themselves, they are either managed by the company or a fund manager, who has no fiduciary responsibility to your financial well being. Finally the social legal reality of any sort of worker owned fund is reveled in bankruptcy(in murica though I imagine it isn't much different in other capitalist hell holes). When a company goes bankrupt employee pensions are almost always last in line for restitution from the sale of company assets. This means that those most responsible for bad management, those who own the stock, will always be made whole on the backs of the worker retirement funds.

Basically I would tell your friends to grow up, learn some dialectics and stop thinking like children.