I do believe it's a mental illness. But I also believe, like you, that there are ways of dealing with it and that ultimately only you yourself are responsible for messing things up, for digging yourself a hole so to speak. I also believe the only one who can climb back out is you. Although some people do need help breaking the cycle, that's a fact. Some people just get in too deep before realizing or being able to admit to themselves they have a problem. The higher power crap is something I don't believe in either, but I do believe that seeking help when you're in way over your head can become a necessity. Granted, it may make other drug users look bad. But no one wants to be dependant and/or addiced to (a) drug(s). It's just a fact that some people can use occasionally, and some just can't. I believe it's mostly acting on impulse that lands people in trouble. But there are people that can't help it. I am very impulsive myself, and I have tried countless times to quit opiates, even with professional help, but I still haven't been able to get over my opiate addiction. That's just to give you an example.
I just think you're painting a pretty black&white picture here while there's so much more to consider.
But in essence, I agree that it all comes down to one's own responsibility. Though I think it's harsh to say that addicts who have a serious drug problem 'ruin drug's reputation for the rest of the population', like I said before, no one chooses to become a junkie/addict. Starting to use drugs is a choice, becoming addicted.. Is not. It might, as you say, make drug(-users) look bad, but it's not like these people are doing it on purpose and I know for a fact that many addicts would much prefer to be clean, and try to get clean, but keep relapsing regardless of how motivated they are.
Not trying to get into a debate here, but that's just my take on it, in a nutshell.