No. ASICs made Bitcoin more secure (and less in a way). Before ASICs, CPU and GPUs dominated the mining scene and if were to still be the case today, there would be large botnets profiting off Bitcoin mining as everyone has either a CPU or a GPU but most won't have an ASIC. The difficulty is in essence a measure of how difficult it is to mine a block or to attack Bitcoin by re-organizing the chain. Proof of work works best if it is significantly more difficult and expensive to attack the network than the potential profits.
Botnets aside, we only have large mining farms as we can have lots of small ASICS in the same place. It wouldn't work with whole PCs. How do botnets get their work into the system? Are they their own pools? Do they just feed into legitimate pools? Can't we blacklist them somehow?