You can be interested in fixing bad behaviour on the part of companies with a lot of power and leverage even if you're not the victim of it.
Sure, you can also do nothing.
That's fine. Unions are democratically controlled organizations and they won't always align with your personal interests. "This specific union does not align with my priorities, so I'll avoid joining" is not something that will aggravate too many activists. "Unions suck and everybody should resist them in general" is what bothers people.