I think they're beneficial for unskilled labor. Unskilled labor doesn't have a leg to stand on without them and that's not right. Workers should at least have some basic means of bargaining collectively with management. Right to work states are the worst, workers are replaced like spark plugs for no good reason and unions are basically castrated. Granted most unions are old, outlived their usefulness, and became corrupt. Because of that it's really easy to convince people unions are bad, but when used properly they're valuable.
So yeah, my two cents on the subject.