What Invention Should We Uninvent?

We were sat outside a Costa during the week enjoying the sunshine and I can't remember how the conversation got around to the subject but seeing as we were a bunch of lefty tree hugging types it was probably something about the evils of Capitalism or something but we began mulling over which invention, if we could, would be uninvent as it has been catastrophic and killed the most people.
My first thoughts were either Religion or guns but then we began bouncing around other ideas and we ended up with a confusingly long list which we probably could never prove but into the proverbial pot was thrown Cigarettes, Plastics, Gunpowder, White Sugar, Cotton Clothes, Internal Combustion Engine, Coal Mines, Oil Rigs, Processed Foods, Printing Press and CFC's.
A few of those we can throw in together so Sugar and Cotton clothes are linked to the Slave trade which killed millions while the amount of deaths from Sugar alone must run into hundreds of millions through Diabetes, Cancer, Hyper Tension etc and processed food also increases Cardiovascular disease, Cancers, Obesity and diabetes and the death toll from tobacco is uncountable.
The Internal Combustion Engine  gave us  cars and lorries, trains and ships so we have all those deaths in crashes and accidents as well as the pollution it throws out which is not only killing tens of millions each year but will do so for the foreseeable future.
Environmental damage from vehicles must be included in Coal Mines and Oil Rigs which provide the material to run the internal combustion engines and all the deaths from those as well as the many deaths from Climate Change.
Atmosphere destroying Chlorofluorocarbons (CFC's), especially ozone depletion and the  exposure to UV radiation which leads to skin cancer or other diseases, were so harmful to humans that they were banned in the 1980's and the Printing Press was one i was confused about until it was explained how the increased ability to read led to dangerous ideas being circulated and deaths from ideas and the resulting genocides and wars.
My Guns was withdrawn and instead we replaced it with gunpowder to encompass all explosives, guns, artillery and fireworks and the number of deaths from those since its invention is astronomical.
Hard to find hard figures to find out definitively which invention has been the most harmful and has led to the most deaths that we should uninvent it if we could and if our lunch break had been longer we probably would have thought up some more but when you think about, some of our inventions sure didn't turn out to be the best idea the inventors assumed at the time.