I agree that gambling is bad and nobody should do it, but that's different from the government preventing you from doing it.

Something being "bad" doesn't mean it should be banned, it means it needs closer scrutiny to make sure both sides of the transaction are fully informed of the risks and can meaningfully consent.

money laundering

I don't like this reasoning because the underlying assumption is that violating people's privacy is okay if it helps catch criminals.

That said, there are typically rules that limit this. In most areas, casinos have to ID you and report any transaction over a certain amount (usually $10k or so per day, many casinos have a lower threshold) to tax authorities specifically to combat money laundering, just like banks do. That seems to limit money laundering for larger players, but obviously doesn't do much for smaller players. To do better, we either need much lower limits, or much higher surveillance, and both would violate innocent people's privacy.

Instead of that, we should take a hard look at policy and policing. For example, a lot of money laundering is by drug dealers, and they exist due to drug bans. Maybe we should consider legalizing and regulating more drugs, which would give people safer options, reduce incarceration rates, and reduce laundering from illegal drugs since more people would go for the safer options. On the policing side, we can improve training, reallocate people from ticketing to investigative work, and build community trust to improve quality of reports.

At the end of the day, I think personal liberty and privacy is more important than preventing harm or catching criminals. I also think we can do both, but we need to start from the perspective of maximising liberty and privacy.