The main result is a secret political funding system called Super PACs. These groups can take endless amounts of cash, making sure that political votes and outcomes are heavily controlled by the people with the most money.
The cost is that democracy gets weaker. When politics is just about money deals, regular people feel like their vote doesn't matter. This leads to people stopping caring about voting and their government.
You lose time to never-ending elections. Since there are no limits on spending, political campaigns get longer and run all the time, demanding constant attention and distracting everyone from actual government work.
This ruling speeds up the process where big companies take control of government agencies and lawmaking groups. This leads to them erasing rules and pushing their costs (like pollution or debt) onto the public.
The problem is Speech Inflation . When a giant company's virtually infinite capital is converted into "speech," it totally drowns out the small, limited voice of an average citizen.