Equating drug addicts with child molesters or serial killers is a tad extreme, don't you think?

No, all of them are negatives upon society with no balancing positive side to them being so*. They may not be on the same level guaranteed, but they are still a danger to all by their existence.

That's without getting into how much cross over group A and B have. I'd wager a large percent of those molesters and killers and every other violent crime (and even many non-violent ones) are on some form of drug.

*A serial killer might be arguably having a positive effect if the killing is of the right people, but that's a very murky and dangerous position so let's ignore that rare possibility.

Being addicted is an affliction

A self-inflicted one, that's what you keep missing. They've chosen to do this to themselves. They damaged their own life and usually the life of everyone around them by their own choices, and its in the pursuit of mostly hedonistic self-pleasure. That is evil in all ways.

That's without even getting into the societal problem, wherein someone has wasted all the time and resources put into raising them to be a productive and upstanding member of society, and is instead choosing to be a complete burden on it.

What's your definition of junkie?

Anyone who does unneeded drugs. Personally, I'd even throw alcohol in with them but people aren't ready to hear that.