Time for a protestant king?

[Schonne]

I can take this decision. It will cost me 2 stability, give me 10 legitimacy and make my king and heir protestant.
What's the point? I only thought culture was relevant to be able to promote advisors. I obviously missed something, but what exactly?

 

[ecrurudesby]

There are a whole host of new events for a country ruled by a heretical or heathen ruler. I don't care to read them all but I expect at least some of them to be harmful to the realm. Presumably your state religion is Protestant? In which case converting your ruler and heir will probably disable some of those events.