Credit card companies. And it's not that they don't care about sellers. It's that they care more about the card holders. Consider the protection they afford card holders for card-not-present purchases. 100% protection.
PayPal doesn't have some immunity to that protection. Open your own merchant account, and you'll have the same issues.
> I see it as simple piracy
When it's the card holder claiming a chargeback for an otherwise legitimate purchase, it's known as friendly fraud. Not so friendly. And generally, it's worse than piracy. Normally you are charged for a chargeback (not sure if PayPal charges you a chargeback fee). So in those cases, you actually lose real money, as opposed to piracy.