That's the point. Using relational data in a non-relational system is just foolish, and introduces issues not worth dealing with. What exactly is MongoDB going to give you over PostgreSQL in that case?
Honestly, spinning up a SQL server really isn't rocket science. SQL is easier to read and write than that messy mongo query language. Though, if you're used to taking the quick and dirty route for everything, you're probably using ORMs anyhow. But why do things twice? Just do it right the first time.
