Sadly, nailit, many of the types of people you describe (people with drug or drink problems) are likely to have criminal convictions which would prevent them being appointed. Similarly, someone with drink or drug problems is unlikely to be able to “understand documents, follow evidence and communicate effectively” or “think logically, weigh up arguments and reach a fair decision” (two of the personal qualities required).
Also, as has been mentioned, people from deprived areas are probably unlikely to feel the need to serve their community in this way (though some do).
If you do your research, Mosaic, you will find that few Freemasons are Magistrates and equally few Magistrates are Freemasons. There is little or no correlation.
Serving as a Magistrate is something you have to want to do, nailit. It is not something you would do if you have no interest in doing so. You are unlikely to see any Magistrates with drink or drug problems simply because of the reasons I outlined. Furthermore I doubt anybody – including you – would want to have a verdict or sentence passed on them by somebody unable to grasp the principles of justice because they are addled by booze or cannabis. I was glad you received restoration in the Crown Court from the injustice you received at the hands of the Magistrates. The right of appeal is a vital part of the Criminal Justice System.
Your contention that if Magistrates had a harder life “…their judgements may be more learned and appropriate” is misplaced, murraymints. In terms of delivering verdicts Magistrate are much more constrained than juries. They have to give reasons for their findings in open court rather than simpy pronounce “Guilty”. When sentencing they are (like judges) bound by sentencing guidelines and have to have good reason for departing from them. If they do so, once again, they must provide reasons in open court.