I think the biggest difference here is that Portugal abolished prohibition, acting with unity as an entire country. That's very different than when cities or states do away with it, but there's unrestricted travel between there and thousands of counties next door or a few states away, where prohibition is in full force. Those counties get hit with not only an "on-steriods" version of the symptom in question, but also any other demographic patterns that are corrolated with it for any reason, such as (in the case of IV drug users) extreme poverty.

One frequent response to this point, is for someone to say "I'm open to decriminalization arguments, but I'm not supporting anyone who says 'The entire country has to adopt my policy in order for it to work!'" Which sounds reasonable, on its face, but in this case it seems like it really is the best option.