Unions are like any other human institution—prone to human failings. But that weakness doesn't mean we should abandon or vilify them. It means we should strengthen them and address whatever corruption we might find. It also does not mean that we shouldn't be proud of the many, many good things that unions have done for working people—the 8-hour workday, the weekend, worker's compensation, safer working conditions, child labor laws, pensions and health care benefits, to name only a few. There's a lot in labor history to honor and celebrate and be proud of.
At one time, labor unions in the United States had more power than they do today, hence their vulnerability to corruption. You know, "Abuse of power comes as no surprise" and "absolute power corrupts absolutely." But now, labor unions can hardly be singled out for corruption and abuse of power. To abuse power, you have to have some. The real point of labor unions is to give power to the powerless, to aggregate against inordinate corporate power.
Nowadays, the search for corruption is an easy one. Anyone paying attention knows that U.S. politicians are far more responsive to corporate lobbyists and monied interests than they are to their constituents. Corporations are writing laws designed to undermine not only workers' rights but those of the poor and the disenfranchised. And politicians are giving their corporate supporters a leg up on the backs of the poor.
In short, my dear troll, if you're concerned about corruption, follow the power. And given that labor unions have very little of that these days, they should be the least of your worries.