Businesses try to hire the BEST people for the job.
Modeling agencies try to get the best looking, hospitals try to get the smartest most qualified doctors, etc. They all have means of judging whether a person is the best for the job.
Why an alcoholic isn't the best person for driving a truck can't be beyond comprehension.
Difference is that you're talking about instances where people apply for jobs. For instance, modeling agencies don't suddenly fire models who've worked there for years if they have no reason to.
I'd be more forgiving of the trucking company if an alcoholic truck driver applied for a job there, because then they'd change nothing about the status quo if they wouldn't hire him. The driver would just have to apply for a different job. In this instance, however, the company is hugely inconveniencing the driver by taking away what's presumably his main source of income, even though he's never made a mistake after five years of employment, just because he's an alcoholic. I'm not OK with that.
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Full rap metal jacket ~ Method Man