I understand, I'm equally frustrated when people including scientists say that something evolved for an environmental specialization, instead of the evolution being happenstance that may have incentivized more viable mutant offspring surviving until reproduction in that environment, but was not "for" anything.

and yes, so I understand that with human cancer, it tends to happen or advance after reproduction has already occurred so therefore those traits are not selected against. it's impossible to weed out with human mating strategies

I would just like to believe the cancer itself is an adaptation preventing something worse, but you're right, it doesn't work with the natural selection theory and so we just had a dead end to our survivability baked in, not so different than how the opposite phenomenon of senescence in cephalopods ends their lives