I'm relatively new here so forgive the naive tone of this question, just because it is simple I don't mean it flippantly, I really would like to know if anyone knows real data.
How many accounts and how must Steem have been saved from malicious actors by the lock down? Ballpark?
Nobody is there to save me if I post my bitcoin passphrase on line, why is a safety net needed here?
It's not designed with the safety of the user in mind. It's designed for the strength and stability of the Steem economy. Among many things, it protects against actions such as pump and dump and other similar fraudulent strategies. If you want details on the specific thoughts that went into this decision, check out the Steem Whitepaper, specifically the Steem Power section.
The essence is captured in the first three paragraphs, so I will quote them below: