In practice I would draw the line at things that are mostly consumed by addicts. So I'd have no problem being a vintner, but I wouldn't want to be a heroin manufacturer, even if it were legal.
There are various edge cases you'd have to treat individually-- e.g. if the median user wasn't an addict but all your revenues came from the addicts. In that case, again, I probably wouldn't want to do it.
Speaking as someone that worked at one of Zynga's main competitors, I can assure you that industry makes 90% of its revenue off 10% of its users. It's a mental addiction to simulated success.
There are various edge cases you'd have to treat individually-- e.g. if the median user wasn't an addict but all your revenues came from the addicts. In that case, again, I probably wouldn't want to do it.
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