I hear that word used a lot over here in the UK, usually by people on right of the political spectrum, but the word sounds rather pejorative to me. I presume the people using it mean "users of drugs, excluding alcohol" in order to differentiate themselves from the users of the other drugs.
And, I think this is confused labeling. Substance abuse alone does not make anyone a danger to you.
So, substance abuse: a) person goes to a daily job, drinks a bottle of wine in the evening, does some coke, goes to sleep. repeats ad infinitum. b) person has a really bad addiction, needs money, so he robs you
I presume your talk about fear and judgement was more about scenario b rather than a, but both are about a person with substance abuse problems. The thing we don't actually like in b) is the stealing, not the substance abuse per se.
If we did that, it would be rational, and an improvement. The unfortunate truth is that we tend to judge people for being outsiders, so while alcohol causes much more harm to others than heroin or crack cocaine (citation below), “we drink alcohol so it must be fine”.
Same with terrorists: if the killer is one of “us” they are “a troubled lone wolf”, if the killer is one of “them” then “that just goes to show how nasty they all are”.
Same with child abusers: “stranger danger” is what people worry about, but most documented abuses are committed by close relatives.
(Relative harm: https://en.m.wikipedia.org/wiki/Drug_harmfulness#/media/File...)
Why this need to judge?
It is particularly odd given a country where such a high proportion claim to be Christian, and perhaps ought to follow the instruction to leave it to their God to judge people.