The case you described, where the cancer cell resulted in the death of the individual human, could equally well be described as kin selection. An individual that hurt its close genetic relatives- and actually actively kills them- also hurts its individual reproductive success.
The argument against group selection is an argument against its usefulness as a concept. Where group selection works, it is mathematically indistinguishable from kin selection, so you might as well use kin selection as your conceptual model. Additionally, it can be confusing for people who don’t understand the circumstances where it definitely cannot work, which is any case where the individuals are not closely related.
Indeed. Archaeological study of the grounds surrounding Stonehenge shows evidence of what appears to be a prolonged conflict between two neighbouring settlements, which lasted several hundred years- during which time there were no new religious monuments made in the area (suggesting that most energies were devoted to this conflict). There’s evidence of several major battles.
(Source: http://www.bbc.co.uk/programmes/b04hc5v7)