That would be good having a toggle for it... but the tech tree should reflect that higher levels of planetary bombardment weapons do not need to be 'dirty' bombs... but rather just infrastructure and population killers or both.
Current real life world destruction revolves around nukes which we all know to have massively negative radiological side effects. But as our technology grows, cleaner weapons of mass destruction should be possible, like the neutron bomb which destroys electrical components.
Who says WMD's have to be so dirty? What's wrong with clean WMD? In fact, what's wrong with a 'cleaning' WMD? One that not only destroys population and infrastructure, but at the same times rid the planet of all blood sucking mosquitos thereby improving planetary conditions?
