Ref to my previous Qn, Do you think people take substances to relieve symptoms rather than it be the cause?

I am asking this because of some of the answers to the last Qn.
Many patients who I nursed often had Mental Health issues long before the abuse of substances. He had 'dual diagnosis' and said it was wrong because the mental illness came first and the substances provided the relief.
I agree with him to a degree but have also seen folk screwed up by drugs.
Kerry Katona is a good example of someone who's life was screwed up before drugs, and more so because of them.
Do people with problems take drugs to fill a void?
Should everyone automatically have the same coping skills for life despite taking an emotional battering and trauma?
Is it easier to blame drug taking as the problem than addressing the underlying cause?
This Qn is in news as I am seeing it alot at the moment. I am also exploring attitudes for my studies and want opinions from 'outside the box' so to speak.
cheers

: http://alcoholdrugstreatment.info/ref-to-my-previous-qn-do-you-think-people-take-substances-to-relieve-symptoms-rather-than-it-be-the-cause