I don't know what you're talking about; is there even a downvote button on Hacker News? I certainly don't see one.

Some features that ORMs make unnecessarily difficult (or impossible without simply avoiding the use of the ORM) to use, off the top of my head:

* transactional DDL

* temporary tables

* user-defined data types

* asynchronous notifications

* dynamic SQL

* non-serial keys

* multi-attribute keys

* temporal schema

* window functions (really all manner of analytics queries)

Those were just the ones off of the top of my head, ones that are not "independent of SQL features."

Enjoy your flat-files, because that's actually what ORM gets you close to: a procedural abstraction inversion over a rich and capable declarative interface and first-order-logic engine.

To answer the downvote tidbit, there is and it shows up when your Karma is high enough. That threshold is not disclosed however.

You wrote, "when you are using an ORM, most of the arguments [against using a different DBMS for testing than production] are obsolete, too," which is false, unless the point of the ORM is to bring the production DBMS down to the test DBMS's level of capability.