Your question is a bit like asking "how does insurance stop my house catching on fire?" - it doesn't; it makes sure you have some protection if the worst happens.
I've worked in private companies where the maximum comp is set by management and they do not allow individual negotiations. And I've worked in heavily unionised organisations where I was able to negotiate a better deal for myself.
Do you really think your unique talents will save you from a lecherous boss or protect you from being discriminated against?
And, if you wanted to sue, how much will an attorney's retainer cost? Hint - probably a lot more than you Union dues!
I don't understand how a union helps with this vs. an attorney. Other reasons for unions, but these items don't seem particularly persuasive to me.
That gets me unlimited legal support.
How much does a typical employment attorney cost per hour?