Question

how far are responsiable for making ourself ill

Answer 1

 If this is a homework assignment and you are on the opposing side of the question, you have your work cut out for you. 
Stress plays a major role in illnesses. This will be brought up and the only response I can think of is; for people who are sane it can become a choice to not endure so much stress by the way we choose to handle each and every situation along with how long we allow our own minds to re-play any bad situations or keep it in our minds. 
Also stress came from an initial problem to begin with and some people can't just turn their minds on and off to keep stress at bay that could potentially ward off some illnesses. 
Many illnesses are caused by the environment. Look around as everything makes or can make you ill. It's in food, water, preservatives, and even healthy things such as insecticides on vegetables and fruit. Cows are given a range of injections to make them "taste better" but what is that doing to our health? 
There are more things we can not control in society that makes us ill than things we can. I believe this is a reason behind many illnesses today along with Autism, Parkinson's, MS, and so many diseases that are auto immune diseases. 
Honestly, I do believe we as humans are capable of causing ourselves to be ill just as much as the environment and other causes. 
Between the food we choose to eat, smoking, alcohol, drugs (legal or otherwise), and lack of exercise along with stress we are a top country in this world in which people do not take care of themselves and in your defense on this topic, we have a horrible health care system which causes illnesses or causes them to go undetected due to lack of insurance or doctors that are not well trained in certain fields that could find out what is wrong with us before going through so much. 
Stress is I believe a number ONE killer so be ready to defend that.