All four examples involve threats - one party threatening to punish another unless the other party obeys some rule - but the last threat (threatening to increase existential risk contingent on acts of forum moderation) sticks out as different from the others in several ways:

1. Proportionality. The punishment in the other examples seems roughly proportional to the offense ($500 may seem a bit high for one album, but is in the ballpark given the low chance of being caught), but over 6,000 deaths (in expectation) plus preventing who-knows-how-many people from ever living is disproportionate to the offense of deleting forum comments.
2. Narrow targeting. Most of the punishments are narrowly targeted at the offender - the offender is the one who suffers the negative consequences of the punishment, as much as possible (although there are some broader consequences - e.g., the rest of the forum is deprived of a banned poster's comments). But the existential risk threat is not targeted at all - it's aimed at the whole world. Threats to third parties are usually frowned upon - think of hostage taking, or threats to harm someone's family.
3. Legitimate authority. There are laws & conventions regarding who has authority over what, and these limit what threats are seen as acceptable. Threats can be dangerous and destructive, because of the possibility that they will actually be carried out and because of the risk of escalating threats and counter-threats as people try to influence each other's behavior, and these conventions about domains of authority help limit the damage. It's widely accepted that the government is allowed to regulate driving and intellectual property, and to use fines as punishment. The law grants IP-holders rights to sue for money. Forum moderators are understood to have control over what gets posted on their forum, and who posts. But a single forum user does not have the authority to dictate what gets posted on a forum.
4. Accountability. Those with legitimate authority are usually accountable to a broader public. If citizens oppose a law they can replace the legislators with ones who will change the law, and since legislators know this and want to keep their jobs they pay attention to the citizens' views when passing laws. Members of an online forum can leave en masse to another forum if they disagree strongly with the moderation policy, and forums take this into account when they set their moderation policy. But one person who threatens to increase existential risk if his preferred forum policy isn't put into place is not accountable to anyone - it doesn't matter how many people disagree with his preferred forum policy, or with his proposed punishment.

I'm not entirely in agreement with the first three threats, but they're at least within the bounds of the kinds of threats that are commonly acceptable. The fourth is not.