Conversely, companies that oppose employee unions should hire and employ only shareholders, with a number of shares commensurate with the importance of their work roles. That door swings both ways.
Unions are not an exclusively socialist construct.
I support unions as an anarchist, because I recognize that it is both useful for corporations with concentrated capital to exist and necessary to counterbalance their power with opposing institutions to keep their perverse incentives from directing their behavior unchecked. If all social institutions are set up such that they check and balance one another, no single one of them can safely dominate. Each has a time to be supported, and a time to be undermined.
For now, government institutions and religious institutions have refused to counter commercial/mercantile institutions, so the lowest-energy path to doing so is reviving the unions. Growing a neo-socialist voting bloc now is a longer play, but that one will be beneficial between 6 and 12 years from now, and probably won't become threatening for 20 years. One can never know in advance; democracy is messy.
Socialism is an awful idea in isolation. It's a great idea if your goal is to temporarily undermine those whose power is based on accumulations of wealth and pre-existing social contacts. If you feel that those in power are keeping you from breaking into their ranks, you can promote socialism to clear them out, and then move into their vacated places of power to quash the socialism before it gets out of hand.
As I am not one of the elite, and do not currently have any plausible way to become one, I fully support a socialist political movement. For now.
My personal morality does not compete well against those whose ethics revolve around "might makes right", "them that has the gold, makes the rules", and "F U, I got mine". So I have a newer rule: to suppress my other ethical rules in all situations where those who do not share them are exploiting my respect for them, and any information asymmetries, in order to influence my behavior to my own detriment.
I have no right to the fruits of your labor, but rights are a political construct. They have to be protected by a chain of support, like chess pieces. And right now, someone has sacrificed all of the pawns. The right to keep one's own property weakens in the face of a growing class of people who are somehow completely unable to accumulate significant wealth, even after a lifetime of toil and diligence.
Middle class purchasing power has been stagnant since the 70s. That's more than enough time for all those getting screwed by the system to forget why they ever believed in it, and to raise children who never believed in it, who then decide to replace it with literally anything else. The seeds for the democratic socialist resurgence of 2019 were planted in the 1980s and 1990s. Sow sighs; reap gales.
I can live with socialism for a few political cycles, if it can clear out some cruft at the top. It's dangerous, and difficult to know when to hit the brakes, but I feel ill used by the current system, and I'm not going to go down with it.