For me, I would choose computer viruses.
2 points
What’s wrong with concrete though? I’ve never really looked into it before, am I missing something important?
2 points
Not sure if this is what the parent had in mind, but concrete is absolutely disastrous from an environmental impact perspective. Not only in the manufacturing process, which is quite bad, but the end result, too. Massive water system disruptions lead to deadly floods and erosion, which lead to further problems. Building massive water dams are among the most disruptive thing humans can do to a functional ecosystem.
There’s also the societal impact from car-centric city design and all of the negative effects associated with that.
2 points