That's a misleading representation of the defense. "If I didn't do it, they would eventually have become a public nuisance in the form of nodes in a botnet" captures the supposed intent more fairly, and with the intent to target every known vector used by Mirai and Qbot it seems quite realistic that these systems would eventually become botnet nodes.

It's IMO somewhat comparable to culling high-risk farm animals to prevent widespread disease outbreaks.