Where there's smoke, there's fire - the existence of piracy and the willingness of people to offer some money in lieu of piracy because of what, a basic sense of fairness and honesty? strongly suggests that the problem is that HBO is not offering enough in the way of tiered pricing.
The trick is, there has to always be a trade-off, so that each tier is equally attractive to some big group of people. You can't have one tier be the obvious winner, or everyone will cancel their subscriptions and go for that.
The trade-off is money vs. time. Pay more money (HBO subscription) and you get the shows faster. Less money, you have to wait longer (which is what Netflix already offers). Put a tier or two inbetween HBO and Netflix and let everyone decide which trade-off is right for them.
All the tiers in the world won't eliminate piracy, but it will certainly eliminate the excuse that some people might raise, that HBO is not letting them hand over their money in the way they would prefer.
HBO is shielded from the market by long-term contracts with major cable providers. It's remarkably stable, and can therefore take large and expensive risks with its programming.
HBO only reaches a small % of the global population with their programming, especially if you don't count piracy. The potential revenue from this massive audience could make up for the loss of stability from those long-term contracts.
However, this argument does have a point that it would cause financial turmoil for HBO to rock the boat. I think it's short-term turmoil that is inevitable regardless because the long-term pressures on all digital entertainment will force it towards being widely available, highly convenient, and very cheap. The history of consumer adoption of technology tells the same story over and over: people use technology to get exactly what they want, and businesses that don't adapt get left in the dust.