I actively encourage my clients not to engage in database dogma. I recommend MySQL for high-replication and high-connection work and Postgres for reporting systems and financial data. I always offer to buy them copies of both out of my own pocket.
I also recommend using more than one language when it makes sense. In my experience the damage of choosing one technology over all others always seems to be worse than the overhead incurred in using more than one.
It is not a question of database dogma, more (for me) that clients depend on my recommendations.
Since it never occurs to them that a database could lose their data, they are not familiar with all the dangers to your data that are "out there".
Foreign key constraints and subselects that work properly, readers never waiting for writers, etc. are all things that most clients don't understand but expect you to.
Do you have clients that hold you responsible for multiple years' worth of content or other data?
Concerning languages, both MySQL and Postgres try to adhere to the same language - SQL.
You're basically repeating the standard line in every respect about how Postgres is a "real" database and no one could ever do anything serious with MySQL. That's dogmatic thinking.
I was speaking of using multiple programming languages, when it makes sense. You probably also insist on one "serious" programming language above all, right?
Why does it bother you that I recommend Postgres over MySQL?
All else being equal, for new development, Postgres is the better answer - that is not dogma, it is based on experience gained over 8 years and not without a few late nights of fixing something. My clients with an existing code base run whatever they are currently running.
I don't have an opinion on the use of multiple programming languages, the purpose of a database is to reliably store data that (usually) some other programming language uses or produces. It's the reliable storage part that matters.
"All else being equal, for new development, Postgres is the better answer..."
That's very thinly disguised dogma. Whatever the question, Postgres is the answer.
It doesn't bother me though, I'm used to seeing people choose one camp over the other. I just wanted to point out that I use both for different things and it's served me very well. The MySQL vs Postgres discussion itself is unbelievably boring.
