Just look at research. The harm rates are stable across countries because gambling addiction is a real addiction, it occurs regardless of governmental structure

Just look at research. The harm rates are stable across countries because gambling addiction is a real addiction, it occurs regardless of governmental structure (but serious harm can be prevented by effective regulation, HK is an example of a country where overregulation has led to massive harm). It didn't use to be manageable before, you probably just didn't hear of it happening. Remember online poker used to be widespread. Illegal sports betting was very widespread. Someone "irresponsibly" losing money isn't the same thing as an addiction either (if you do research into why people get addicted to gambling, you will find out that it isn't about money, it is often about sensory experiences which sports betting does not provide).