I don't think this is inherent to the idea of a union. Unions should be democratic (I don't defend unions that don't give a shit about democracy), and tend to b

I don't think this is inherent to the idea of a union. Unions should be democratic (I don't defend unions that don't give a shit about democracy), and tend to be quite concerned with process. If the union wants to support the accused and not defend the harasser that's their perogative, and if you don't like how your union handles (or doesn't handle) these situations you have the ability to lobby your union to change its process.