Are you suggesting casino and bookmakers' clients derive no utility at all from gambling? In the absence of any enjoyment or other benefit, who forces the clients to participate?

Same argument can be made for tobacco salesmen, drug dealers etc. If people pay money for something then they MUST derive some benefit from it... I find that assumption questionable.

Other things I could mention: multi-level marketing, snake oil sellers e.g. homeopathy astrology etc.

I find the assumption that every casino and gambling company in existence provides no benefit, of any kind, to any of their customers....extremely questionable.