It's getting a little tedious going round and round on this. So far the only argument I hear is "We need the post office because the government is s'posedta, you know... mail things." But what I do not hear is how we can afford to pay for it, or why it is strictly necessary in the same way as firefighters or police.
The world will not come to a grinding halt without the USPS. The free market will provide an alternative. It just won't come with the same pleasant memories from your childhood that provide you with a false sense of security the way government mail does.
So, setting aside all appeals to emotion, there is only one real solution here: drastic cuts to the post office. But considering that the emotional appeal usually wins the day in American politics, let's just keep throwing money away.