Earlier quoted context omitted.
There's a really amazing book by Susan Sontag, Illness as Metaphor (and a followup she wrote in the late 80s called "AIDs and its metaphors") which talks about this need to speak about disease as a conflict or fight, or as a foreign invasion or corruption. It's a fascinating book also because it compares the 20th century ways of talking (or not talking) about cancer with how tuberculosis was discussed in the 19th cen…
Except that cancer and infectious disease really are conflicts and invasions, no metaphors needed. At the cellular level you really do have cells killing cells based on recognition of whether they are not they are recognized as "self".
See also my comment to ubernostrum further downthread. There is no compelling reason to frame cancer or infectious disease as a conflict or invasion. Doing so is just as reasonable as framing housekeeping as a conflict with 'foreign dirt' or an invasion of 'the outside world into your house'.