Should tobacco companies be held responsible for smoking-related illnesses and deaths?

Not at all. If you smoke or chew tobacco, you're making that choice. It says right on the side of all tobacco products "Surgeon General's Warning: Smoking May Be Hazardous To Your Health"
Seriously, people who smoke know what they're doing to themselves. Tobacco companies are only doing their job. It's the people's decision if they use the products or not.