I think one of the primary motivations for cryptocurrency was that legal ≠ moral. Therefore, I think cryptocurrency's best use cases are all explicitly illegal.

For example, you can donate to Sci-Hub with cryptocurrency. Sci-Hub has an ideological mission which is widely supported, but it runs afoul of copyright law and is illegal in nearly every country and sanctioned in many. You cannot donate to Sci-Hub with fiat currency.

Unfortunately, I agree that in practice >99% of cryptocurrency's use is for scams.