From my observation and knowledge over time I think your statement "prone to addictive behavior to begin with" is correct.

That said I'm not reading what you are saying the OP is possibly suggesting at all.

He says:

"One of my relatives, for example, managed to get herself off of drinking and smoking completely and was in counseling. The addictions, and the kinds of behaviors that come with maintaining addictions (all kinds of dissociative, anti-social, manipulative weirdness) were ruining her life. Strange thing was, after removing the substance, the behaviors persisted."

I don't see anything that suggests that the initial addiction caused further addictions at all in the above paragraph.