One aspect of this is that it incentivizes Denial-of-Service attacks. It would allow any attacker to directly convert a DoS attack into money. Imagine that the 5 largest ISPs in the United States decided to surveil Bitcoin usage on their network and and record a list of probable addresses for their users (BTC has no transport encryption in its P2P layer). Then, all 5 decide to collude and block the Bitcoin P2P protocol for a week. How much BTC would they earn by doing this? It's a contrived example, but DoS is a common weakness in cryptocurrency protocols in addition to being fairly easy to execute in a typical network context to individual targets. In effect, instead of authorizing transactions based on ECDSA, you're relying upon key liveness which is a much weaker thing to rely upon and would incentivize large amounts of fraud and abuse.