The man-made object responsible for the most deaths worldwide is the tobacco cigarette. It isn't even close.
Tobacco kills 443,000 Americans a year and 5 million people a year worldwide. This is more than the total number of people killed by cars and firearms combined. Cars kill about 32,000 Americans each year and 1.3 million people worldwide, while firearms kill about 32,000 Americans each year and "several hundred thousand" people worldwide.
100 million people were killed by tobacco in the 20th century. This is more than the death toll from World War 1 (17 million) and World War 2 (50 to 70 million) combined.
From a strictly utilitarian perspective, would there be anything to be gained by, say, starting a campaign of assassination against executives of tobacco companies?
Also, the question would be less visible if asked in an Open Thread. Writing it as an article makes it seem more... official? ...than writing it as a comment. At least, if I would read a different website, I would take articles as stronger evidence about the community than isolated comments. The articles are supposed to reflect the ideas of website owners; the comments could be from anyone, and often they are contrary to the ideas of the website.