I feel like things like this are a fundamental social problem. How can this be prevented?
It is highly unlikely this is going to happen.
Addings more laws tends to help the people who can afford lawyers.
You could look at simplifications instead, eg change the voting system from first-past-the-post to something like range voting, and candidate behaviour (and thus reacting to incentives) would completely change.
No one claims they're people. The law lets them stand in as people so society can function. The whole "corporations aren't people" meme is myopically fixated on campaign finance, ignoring the much larger issues around this legal doctrine.
Can a corporation own property?
Can it own patents? Copyrights? Trademarks?
Can it be sued in court?
Can it file lawsuits itself?
Can it make contracts?
I don't think any of us would like the result of answering "no" to all those questions, yet those are the questions that the legal fiction of corporate personhood was invented to answer.
Should corporations have the same free speech rights as people? I can see an argument for answering that "no", as rich corporations may speak disproportionately powerfully. I can also see an argument for answering it "yes", in the sense that corporations are just people acting together, and collective speech should be just as protected as individual speech.
https://en.wikipedia.org/wiki/Corporate_personhood
Remember that whatever constraints you put on EvilCorp's speech are going to apply just as well to the Sierra Club, a labor union, or the NAACP. I honestly don't know if that's a tradeoff work making. Maybe it is.
I agree with your point about transparency.
The worst punishment any company receives for bribing, stealing from, defrauding, or poisoning the public is a slap on the wrist that is outweighed by the profit they make committing crimes. We need to be comfortable with devastating corporate punishments (company-destroying fines, mandatory company breakups, nationalization, jailtime for executives, asset seizure) to have any effect at all. What did we learn from Equifax? Don't worry about the security of people's data, there is basically zero real consequence to posting sensitive data on every citizen in plaintext on the Internet. Money spent on security is a waste, an objectively bad business decision. That's what our government and regulatory bodies have told us. And it's what the market has told us as well, but we already expected that -- we expect the market to choose evil when given the choice, every time. That is its function.
Right now, a CEO cannot say to their board "Yes, the cost/benefit analysis and market forces suggest we should bribe the city officials and steal money from the taxpayers, but we'd go to jail so we can't" because it is not true. All they can say is "it is morally wrong" which does nothing except get that uppity CEO fired so somebody who really cares about profits can be brought on.