In any of those scenarios, the "bad" actor would need to purchase relatively large amounts of STEEM in order for their plan to "work" effectively. But purchasing that STEEM is actually beneficial to STEEM and its user base, so I don't think the damage would matter much, especially once their behavior is exposed. If there is a much larger user base and the platform is as popular as these scenarios assume, then there should be plenty of users to counter those single "bad" actors.

In other words - these scenarios don't seem plausible. Someone trying to harm the network would first need to support it with their own money. And if they did that, their plan would likely fail anyway.

Also - this assumes that a single blogging platform will be the most important element of the STEEM blockchain. I don't believe that this will be the case.