Sure, but why add one more variable to the equation? Eschew additional complexity. As long as I live in a "right to work" state and there is plenty of demand for the kind of work I do, I'd rather deal with companies on a one-to-one basis. If company treats me unfairly, I quit and go somewhere else.
And while the company may not be "on your side", companies are still bound by market forces, on both sides of the equation. You can't compete (for now!) without people, and if you constantly run your best people off by mistreating them, you aren't going to be very successful in the long run.
If that was actually true, employee abuse would be essentially non existent, especially in large successful companies, and unions would have little reason to exist.
Real life isn't that simple. These things aren't binary, "it's true" or "it's false". There is a continuum along which things vary. The extent to which companies are compelled by market forces to treat their employees well is obviously something that varies by sector / geography / profession / etc.
I'm not saying that nobody is justified in joining a union, or that unions have no reason to exist. I'm just saying that relative to my combination of the above factors, I do not find any appeal in the idea of joining a union, when you balance it against the associated negatives.
And while the company may not be "on your side", companies are still bound by market forces, on both sides of the equation. You can't compete (for now!) without people, and if you constantly run your best people off by mistreating them, you aren't going to be very successful in the long run.