Sure, hoarding sucks, but there are ways to deal with that behavior that don't involve price.

What ways? Government controls? Laws that people will ignore when convenient? Penalties that will invariably hurt only the poor without the means to fight or ignore them (rich people will pay fines or pay the premium to buy extra X; poor people can't, and will get shafted)?

For your diapers, why would you give them away in the first place? Because you're a good person? Great! Capitalism won't stop you (or me) from being generous with our time and resources. People who will be charitable and give things away will do so anyway.

However, attaching an incentive for things will increase the supply -- people with things who might not have been willing to share might be willing to sell (thus increasing the supply of goods, which is what matters); and for people who have paid for things previously, why shouldn't they be allowed to at least cover their costs?

What's the alternative -- force people to give away their diapers with no recompense? How is that different from theft? Is there moral hazard in saying, "You have X. I don't and I need it more than you, so you should give it to me"?

So I agree that gouging is morally repugnant, but I can see an argument that nothing would get a flood of supply into a market faster than high profit margins (thus driving down prices). You could slap a special tax on profits from price gouging that would fund disaster recovery etc etc, but any time you have money going through an agency you increase graft, which has its own hazards (which might be acceptable).

Everyone acts in their own self interest. There's literally nothing you can do to stop it. Ideally you incentivize behaviours that generate the best net benefit to everyone. The trick is figuring out what the fuck these are.