HR serves to protect the company, you have to think in HR's shoes. If the complainant goes away and finds another job the problem is solved. Most harassment cases tend not to end up in court, usually the aggrieved party quits.
"HR serves to protect the company"
In a reputable company, HR will pass the message higher up (probably off the record), and a manager will look at the evidence and make a good judgment. In this case, the evidence is clear, the manager should have been fired, and the employee given a sincere (but not in writing) apology and compensation.
Note that HR is a legal role. HR will never advise an employee to consider filing a lawsuit against the company, but instead dissuade the employee by saying that there isn't good evidence, it was an honest mistake, he has a family to feed, try to work with someone else. The saying exists because advice from HR is not in the employee's best interest.
Yes. It's also human psychology. See the church sex abuse scandals. The morality that people claim to have is less important than protecting the group.
The same thing applies to HR. The HR person who shuts down an accuser is doing it in order to protect their position in the hierarchy, and to protect the people in the hierarchy that they know. The fact that it's illegal, and can very well destroy the company is completely irrelevant.
In these cases, short-term focus is more important than long term goals.
While it's true HR is there for protect the company it's false to say that if a complainant just "goes away" that the problem is solved. HR also has to ensure the company keeps a good culture, avoids lawsuits and stays a great place to work for the majority to ensure talent is not only attracted but kept.
Thinking about ignoring or making complaints just go away isn't protecting the company. It's literally harming the company and its employees.
Not if they go on to write a blog post that reaches the top of HN.
HR, done ethically and applied consistently, protects both the company and the employees. It makes clear what is acceptable, and what isn't. And it makes clear what is expected of each employee in general.