Posts like these are a point in favor of "people read last page of posts, not the full thread". It has been mentioned over and over again that religious conversion does currently cost points.
Most countries have 1 Missionary. Unless you're sitting purely in the parts of Europe that start catholic (so no conversion malus from Orthodox/Muslim), 1 missionary isn't really going to keep up with rate of conquest.
More missionaries can be acquired by taking religious ideas (ADM points), DotF if Christian/Muslim or Counter-reformation if Catholic (+tech costs = all MPs), or conquering various religious centers (ADM/DIP points)
Missionary Strength can be acquired by decisions or by taking religious ideas (ADM points).
Catholic/Protestant/Reformed are handheld with +missionary strength decisions that have no cost direct or opportunity. If anything, remove or re-balance those, for everyone else there is already a cost to effectively convert territory.
That stil doesn´t change the fact that converting is just something you just do without thinking too much.
And you are wrong, missionaries cost points conversions don´t.
Even then, lets go with the idea that religious conversion is spending monarch points over the monarch points that you have already invested in Religious to get more missionaries + strength.
Then, its working like Influence in that you spend Diplo Points to save Diplo points, or with admin where you spend Admin points in saving admin points.So its perfectly consistent with Coring, Culture conversion and Diplo Annexing. So its not really an out there concept.
so yeah as it is, Religious conversion is a no Brainer most of the time. Now compare Small religions vs small cultures. One tends to disappear much more than the other.