Totally agree with you there. An oppressor and a wrong doer will use anything, even religion, to get his/her way and that doesn't mean its the religion that's to be faulted but the one who twists it to suit their means. A man can even treat his wife unfairly even if he has just one.
See what a lot of people don't realize is that in Islam we believe we are created to worship our Lord and that every one of our actions be it marriage, loving one another, bringing fourth and bringing up children, doing good by others, etc are all done seeking the pleasure of God. So if we want to gain His rewards and be saved from His punishments then its upon us to act accordingly. And oppression is one of those grievous sins that we have been warned about time and again. So if anyone does so then he will sooner or later get his recompense.
Another fact I wish to make clear is that not every woman will see marriage or even polygyny in the same way. Many of my friends who have co wives will any day list to me the benefits they have of such a marriage. Like take for example a friend of mine who recently right after giving birth to her sixth child was hospitalized. It was then her co wife who took care of all her kids and her own as well and she did so with happiness. They love each other like sisters and hence support each other the way one would support their own sibling.
Marriages are always diverse and one should not judge another's marriage based on how their opinion of how an ideal one should be. Provided everyone is happy and there is no mistreatment and oppression, live and let live I say.