It is often argued that without the constraint of money, more people would indulge in more ostentatious consumption. Maybe this would be a problem, but to hold it up as a fatal flaw given all the disadvantages of the current system is special pleading.The first assumption made here is that people would still want ostentatious things in an RBE; they would still want to flaunt as if they had monetary advantage over others. This suggests no change in attitude and is used to hint that there will have to be some kind of control imposed and therefore someone 'in charge' deciding who can and can't have what. Ergo and RBE is a command economy, statist, communist, etc, etc.
Someone I was debating with on Youtube used the idea of a private ice rink in ones basement as an example of ostentatious consumption. It will serve. Supposing you woke up in an RBE and you thought "I would like a private ice rink in my basement". Let's assume you have a basement and don't mind dedicating the space in it to this frivol. So how do you go about it? Are you going to acquire the materials and build it yourself. In an RBE, it is posited that robots will do most work. Who will have designed and programmed a robot to build skating rinks in basements. If such a robot does exist, you would have to reserve use of it.
Or are you going to get people amd machines to come and build your rink? Why will people do this? They will do what they want to do, which probably won't be building something they are expressly excluded from. And how will you keep the rink private? You will have to take measures to physically exxclude people from it - security. Assuming you won't want to skate on your own always, you will probably want to grant access to those who live with you/are related to you or your friends.
This is a lot of effort to achieve rather pointless exclusivity and ostentation. If you proposed to build an ice rink in your neighbourhood for all to use, there would be a much smother path. It would be an easier construction project, and people would be more likely to help if needed as they would benefit from it when it opened.
The implication of my co-debators poin was the energy usage of all these private ice rinks. I don't know how much energy they might use, but as I don't accept that there would be such a desire for and ability to acquire such ostenatatious things, that may not be an issue.