If you want to dive deep into what viruses aren't, read the book AIDS, Opium, Diamonds & Empire by Nancy Turner Banks, MD. Her second book, The Slow Death of the AIDS/Cancer Paradigm and the Apocrypha of the Eukaryotic Cell (2016) is written for serious health professionals, but a determined lay reader could get through it, with enough rests. For all those virus hunters (viruses have never been properly identified under a microscope), this paragraph, taken from page 8, puts things in perspective (with certain punctuation emphases added):
In classical genetic theory, DNA is the center of the cellular universe and controls all heritable expressions of phenotypic change. It was posited under this theory that information transfer at the cellular level was unidirectional. That is, that DNA transcribed into messenger RNA, which then follows with what is defined as translation -- the ribosomal assembly of amino acids into proteins. In 1970, an enzyme was discovered that contradicted the basic tenets of the unidirectional principle of the theory of information flow from DNA to RNA to protein. The enzyme was reverse transcriptase. It was ascertained that this enzyme was able to transfer information in the other direction by catalyzing RNA into DNA. Given that in molecular biology circles, DNA was seen as the immutable driver of cell function, this was a startling and surprising discovery because it challeneged the prevailing idea of the cellular hierarchical relationships. However, rather than reconfigure the theory, it was erroneously posited by some researchers that this enzyme could be used as an indirect marker for an oncovirus because the cells in which it was found were being used to study cancer. Therefore, the conjecture was made that cells became cancerous by being infected by a virus. So instead of revisiting a dogma about the stability and central role of DNA in the cell and the unidirectional flow of information, the ad hoc idea of a cancer-causing virus was used to explain this new discovery; and oncoviruses became retroviruses, thereby creating more confusion about the genomic response to stress. The explanation given was that the viral RNA would be converted into DNA by the RT enzyme, and the proviral DNA could then be inserted into the genome, thus initiating cancerous transformation. After the discovery of reverse transcriptase, virologists again -- by consensus -- mistakenly began to use and to convince themselves that finding reverse transcriptase in cell culture was the definitive indication of the presence of a retrovirus. However, this time, the same entity no longer caused cell immortalily, but caused cell death. This highly speculative assumption without scientific proof has become virology dogma.
