There is no implication that a thinking, rational being would do what's best for all, only for himself. That in and of itself is NOT a problem, provided he acts honestly, respecting the rights of others as equal to his own. Government's job is to see that that happens, by HARSHLY punishing those who violate the rights of others in furtherance of their own goals. That is what no longer happens. For example, arguably I have a right to clean air, but companies can pay the parasites for permission to foul the air we breathe. Only when it gets bad enough for enough people is that changed. Or, the parasites make rules about what people may not do, for example listing a hundred things you may not dump into the water. The 101st isn't on the list, so if it makes someone money to do it, he will until / unless it gets added to the list. Same thing with all kinds of unethical, immoral, or dishonest behavior. Until it's on some list, it remains legal. "Don't be dishonest. Don't lie, don't cheat, and don't steal" are apparently too hard to understand, so more and more lists need to be enumerated, creating a "shell game" that the dishonest and their parasites can use to their advantage.
At this point I would highly recommend the collection of essays entitled "The Virtue of Selfishness," which is a part of the Ayn Rand library. The topics, covered by numerous authors, address a wide variety of circumstances and explain how a rational individual would determine how to act. Hint: it doesn't involve checking a list somewhere, and it doesn't involve getting permission from parasites.