Humans have been eating meat for at least 2.5 million years, yet cancer has only jumped up to the epidemic it is today in the last 150 years. Something in the environment and diet has changed, absolutely. What is the causative factor? The anti-meat papers with weak relative risk tells me that its not the meat, we should be looking for a very strong signal (50% of people born today will have cancer in their lifetimes - 150 years ago basically nobody got cancer).

Life expectancy in 1875 in the USA was 39.41 years. The vast majority of cancers will not cause significant illness (or show up at all) in population groups that die of other disease/injuries before 40 - so, handwaving away the studied correlative links with cancer in population groups today that eat a lot of meat just because 'people ate red meat 150 years ago and they didn't get cancer' is what scientists call 'illogical'.

And that's completely ignoring the fact that we have far advanced medical technology in the last 150 years so we are actually diagnosing more cancers because we're finding them when they are smaller and more treatable (that's a good thing).