The usual example given is ‘defund the police’. If you’re rich enough to hire your own security or otherwise live safely in a world without police, you can advocate for this and win social points for doing so. Meanwhile, the actual consequences of such an idea, were it to be implemented, would be catastrophic. Unlimited immigration/open borders is another one: if you’re relatively poor, your ability to make a living (among other things) is potentially threatened by this. If you’re rich, you needn’t worry. You can live in your fancy neighbourhood far detached from the consequences of such policies, so you can freely hold such positions and even frown upon those who don’t.
Luxury beliefs are just like tangible luxuries [*] — you have them not because you want them or really believe in them, but because they signal to others that you’re of a certain class. Poor people can’t have them, so they’re desirable as status indicators.
[*] OK — some ‘luxuries’ are worth it and aren’t just for showing off. But I’m talking about the ones that are.