I do not doubt that cancer can be caused by a virus, but we are forgetting that there are many carcinogens other than viruses and multiple causes of cancer.
I never said that the only cause of cancer is viruses. I said the MAJORITY of cancers are caused from viruses. There are other causes including bacteria, fungi, very rarely parasites, radiation, and yes other carcinogens. Although I feel that most carcinogens are not causes of cancer but rather promoters of existing cancers. For example Premarin used for estrogen replacement therapy is a carcinogen. But this estrogen is 3,000 times more powerful than human estrogen. Does this mean it causes cancer? No. Are estrogens known to PROMOTE the growth of EXISTING cancers? Yes. The same can apply to other carcinogens that are actually strong estrogens such as DDT and dioxins.
I cover some of the known causes of cancers here so you can see I do not think that viruses are the only cause: