I think, ultimately, this boils down to a few core questions:
1) Do you believe money is free speech? The Supreme Court ruled in Citizens United v. Federal Election Commission that corporate funding of political campaign ads can't be legally limited because corporations are protected under the First Amendment. Glenn Greenwald (former civil rights attorney, current liberal political blog icon)
basically made the point that a law that violates the Constitution can't be upheld simply because the law produces good outcomes, therefore the ruling, while possibly disastrous, was the right one. Not being an attorney myself, though, I don't find this argument particularly compelling. I'm not sure how the Constitution would matter if corporations ran the United States government, and clearly corporate influence has already caused numerous violations of the Constitution, even just in the last decade.
2) What are our alternatives, and which is the best? In the United States, the primary source of campaign funds comes from individuals, followed by PACs (hard money), however advertisements and donations to parties and other political activities (soft money) are primarily funded by corporations, political organizations, and unions. This leads to certain imbalances. Alternatives to this system generally involve public financing. Clean elections, for example, are entirely free of private money. As to which is best? I really don't know. Just as the American system is complicated and difficult to understand in its entirety, other countries, from Canada to Germany to France are also quite complicated and objectively comparing them is difficult to say the least.
3) How can significant campaign finance reform be accomplished? This may be the most difficult question of all. Various attempts have been made, however many of them have failed because of entrenched interests. The way campaign finance works now is to the benefit of those who have the power to change it, namely members of the House and Senate, and the President. While some individuals are able to choose principle over self-interest, it's been made clear time and again that most don't. The strategy then becomes making it in the interest of these individuals to support campaign finance by threatening their power, be that through elections or through preventing the individual from otherwise profiting from the campaign finance system. Unfortunately, the level of organization necessary to pursue such a thing is incredibly difficult to attain and then maintain. While this in part due to apathy, it also has to do with #2, in that not many people are educated on the alternatives, and even among them, there's disagreement on how the current system could be changed for the better. The best chance I can see currently are the numerous movements which came into being in the wake of Citizens United, which want to create a Constitutional Amendment or otherwise undo the consequences of the ruling. Still, the amount of money and manpower necessary to accomplish such a thing is unlikely to come together.