Most people joining unions are concerned about horrible working conditions and lack of basic respect and rights. The stock price should not be put above basic decency.
Negotiating solo against a large organization with an available labor pool is the weakest possible position, even if the type of talent is in demand. I'd argue that people always want the power in compensation negotiations that's only obtainable by forming strong associations. It's just a matter of whether they can get it or not based on the political power of their counterparties. This type of conflict has been happening since the dawn of civilization.
This is all opinionistic, but use a bit of logic here. Ask yourself what a union is and what the incentives are.