I think that many people in Michael's life were to blame partly, including himself. He was exploited and ridiculed for much of his life, why did no one protect him? After what he went through, it's no wonder he turned to the pills - he was clearly suffering both physically and mentally, needed sleep, was stressed etc...
If Michael had gotten the help he needed, when he needed it, maybe things would have turned out differently. But just like when you reflect on one of Shakespeare's tragedies, you can almost see where his life would end. A kid who was never given the opportunity to grow up, forced into a world of racism (at the time he was young) and a celebrity world of appearances and sex as the most important thing, is there any wonder he may have cracked under all that?
Had he been protected from it by those who were supposed to care for him, he may very well still be alive now.
We need to take into account that Michael obviously saw no other way out. He can not have been completely sane to have needed the drugs so bad in the first place, and so, his actions were almost blind. He should have thought of the kids, but at the same time, I believe his cry for help was many years back, around Dangerous, Will You Be There, and then, after the allegations were made. After that, I think it was only a matter of time (now that I am able to process that he really is gone) that he would have died anyway. Whilst I believe he was one of the most courageous men, he was not strong enough to cope with what he had. Michael was definitely partly responsible for his death. It really depends how you mean by responsible though - long term, then partly yes. He made his choices in life, he trusted the people he did, and whether blindly or not, those choices were still his and we wouldn't have had them any other way, as fans, because it would mean he wasn't the same person.
As for how he actually died, the doctor should have taken more care of him. Michael needed help to get over those drugs and obviously wasn't in his right mind. From what I've heard, he had a pretty crazy day, really agitated etc, and needed the drugs to calm him down. Had the doctor been more careful, he may have survived that night, but I think the shows would have killed him anyway.
Edit: Going on from what Ghost said, from a certain point in Mike's career, he lost that spark in his eyes. He lost that life in him that we all loved. He turned to the drugs as a last resort. I believe he felt no other way out. He was lost, trapped, suffocating. The word death is horrible, but Michael is in a better place now, where he can no longer be tortured by the life he felt so trapped in. People are quick to say he shouldn't have taken the drugs, and to some extent no, but they are forgetting that he obviously saw no other way - he was so far gone that he probably didn't care any more - he was existing for the point of existing. And what kind of life is that? We take a selfish approach to this believing he shouldn't have taken them, but without, who knows how much more he may have suffered?