The blog isn’t really an argument against MongoDB however. In many ways it’s an argument for MongoDB considering if you’ve built a JS based application MongoDB

The blog isn’t really an argument against MongoDB however. In many ways it’s an argument for MongoDB considering if you’ve built a JS based application MongoDB minimizes any additional learning and having to translate between the objects on the front end and in the backend. Non relational DBs are also easier to scale horizontally without requiring any application changes. The OP is an argument against introducing new technology without a significant clear benefit. It’s basically saying that simply having a new tech can add significant complexity, unknown unknowns, and require much more maintenance and other costs. So if your web application is currently running on MongoDB and it’s running well then this is an argument to stick to MongoDB instead of say migrating to postgresql going forward.