The arms industry and intelligence agencies because in both cases it's impossible to even fathom if the work you do for them will be used for good or for harm.

The arms industry and intelligence agencies because in both cases it's impossible to even fathom if the work you do for them will be used for good or for harm. I wouldn't necessarily have qualms working for the military as such (although I'd have to think about it in each specific case), which of course is at least somewhat paradoxical given that I wouldn't work for weapons manufacturers. While often politically controversial, the military also provides a useful - and probably and unfortunately necessary - service to society. Gambling because the products and services the industry provides often not only don't benefit the customer but often are downright detrimental to their well-being. One could argue though that brick-and-mortar casinos at least sell an exciting experience, so the case might not be as clear-cut as with online gambling, for example. Finally, scam industries such as homoeopathy (which unfortunately is rather widespread in Europe) because their products don't benefit the customer.