Yes, gamblers should take full responsibility just like shopaholics, alcoholics and other people with addictions. If we start dividing this responsibility between those who advertise (of their product which, when used in reasonable quantities, does no harm) with people who consume it uncontrollably and face unpleasant consequences, we will harm all parties.
Same in cigarette advertisements - "smoking is dangerous to your health"
Same in liquor advertisements - "drink moderately"
Some gambling sites also have a banner or terms pointing to "gamble moderately" or "responsible gambling". Since these companies are promoting their products and services, obviously they won't say stop doing this or that.
We, as a consumer and clients, should be responsible for what we are doing.
Even if they don't say stop gambling, saying gambling responsibly is already a big thing so I salute all gambling companies that have this warning. They are not afraid that people will follow it, making their incomes to get lessen. In the meantime there are still hard headed people that won't follow this advice or any other advices that they hear from their colleagues.
In the story that OP brought to us, the guy would end up his gambling journey if not because of that single email he received. I salute that act because it shows that he is willing to change but scamming your family member or even other people is still not right but I hope he will also stop it. We can give this guy another chance to change his life.