This is another "Bitcoin will fail because it's successful" type argument (it's usually about hoarding -- bitcoin will fail because it's so successful that people keep them).
The author's argument is wrong because Bitcoin the network doesn't care in the slightest how many miners there are nor how much they are paying for their electricity. It is absolutely excellent for Bitcoin if a load of botnets start mining -- the blockchain is more secure. It's not great for the people who are having their resources abused to do so; but that is their problem.
One could operate a mining botnet and slowly lower the Bitcoin market price by regularly selling small amounts of bitcoins with a declining price.
He should give it a go. See how quickly his ever cheaper coins get snapped up. The price is set by the market, not by the miners. That becomes more and more true every day while we are in our strong inflationary period.
The only potential risk is that a large botnet gets switched off suddenly and the rest of the network can't adjust to it fast enough. Block production would suddenly slow massively. However, I think I saw Gavin writing about having potential work arounds for that, so let's not worry too much.