There's nothing wrong with blocks that only contain a coinbase transaction, they still add proof of work to secure the block chain.
Blocks with transactions ALSO secures the blockchain AND additionally provides the service bitcoin is destined to.
OK, fair enough. My comment above was simply meant to point out that zero-tx blocks, while not optimal, still provide
some service to the network. I don't think this is something worth worrying about. Let each user and miner (including the presumed botnet operator) decide what they want to do. As a user, I am comfortable with any of the likely outcomes. Not a big deal, really.