Corruption comes in many forms, yes. But a private sector union that can elect gives the people they elect incentive to grow the union membership and therefore consolidate power. You can’t elect the person you’re going to negotiate with. It’s pure corruption and a major conflict of interest.

Private money has major issues too but it doesn’t have a direct influence on votes. A company can lobby all day and give money and that might get you more ads. But aligning with a union gets you votes and will continue to.

Police unions do this with Republicans as Teachers do with Democrats.