Unlimited Campaign Contributions and Lobbying are by very definition buying political influence (i.e. pay money to make politicians do what you want), which is the definition of corruption[1], and clearly is not how a democracy is supposed to function.
In a functioning Democracy citizens vote in politicians who share their views, so leaders are chosen based on what people want. When money comes into it, the whole thing gets screwed up. i.e. Comcast just pays millions (billions?) to make sure the politician in power votes for blocking community broadband. Even if the citizens vote out that leader and vote in a new one, Comcast will just pay the new person.
Thus it's corporate money that makes laws, not citizens through voting.
[1] After spending three years in 35 different countries in Africa, I've come to learn the developed world is just as corrupt as many African nations, we're just adverse to using that word because it sounds so dirty and uncivilized. I think it's important to call a thing what it is, lest we succumb to newspeak, so I call out corruption when I see it. Just because it's legal, it doesn't mean it's not corruption.