What if a malicious user performs a Sybil attack of verification (not mining) - spawning a large number of non-mining nodes that verify and approve malicious transactions within a shard.
It does not cost much to create a lot of non-mining nodes, and if the number is huge enough it is very likely that a shard is full of them.
If they are not participating in the consensus, then what damage do you expect them to do? They would only be ‘approving’ invalid transactions for themselves.
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