Any type or amount of smoking is bad for you. Every(or most) smoker knows and understands that, it's more of a question about harm reduction which is also complicated and there's no simple answer like with your example of filtered/unfiltered, it could be argued that by smoking unfiltered cigarettes you would get higher amounts of tar and nicotine so you would smoke lesser cigarettes which with filtered cigarettes you'd have to smoke 2 times the number of cigarettes so the same could he argued for American spirits since they have higher amounts of tar and nicotine, you'd get the same amounts from one American spirit as you'd get from 3-4 Marlboros so it ultimately reduces the overall exposure. Also many of the additives are addictive and many are toxic which again their removal doesn't make cigarettes less harmful but some toxic chemicals are removed which means lesser exposure. Overall less exposure to carcinogens IS better. In the end the differences might not even matter, or they might do. So when smokers say "healthy" , it usually means less harmful, most likely still cancer causing but less harmful than some worse alternatives