That’s not exactly what they held. They held that the President is immune from prosecution for official acts. Prosecutorial immunity doesn’t mean his conduct is not unlawful; it means he can’t be criminally prosecuted for it. That distinction is important because it doesn’t prevent courts from issuing injunctions. And, as stated by others, the immunity is extended only to official acts. What constitutes an official act isn’t super clear yet, but I think it’s safe to assume that golfing isn’t an official act.
The Roberts court invented the official acts immunity out of whole cloth for the sole purpose of keeping Trump out of jail. They're quite capable of interpreting everything he does as an official act.
Sort of. He would still be breaking the law, it’s just that if it’s an ‘official act’ then the judiciary can’t do anything about it, just Congress via impeachment.
I think that opinion would have been less controversial if the President hadn’t openly advertised his intent to violate the law repeatedly. It’s not like the courts are rendered powerless if the President violates the law; any judgments they render are still binding on the parties, even if they require the parties act in ways contrary to the executive’s interpretation of the law. That still means something as long people continue to respect the judiciary. The dangerous game we’re playing is finding out whether that respect will continue.