No I disagree. This is exactly what I want. People who don't have a religion for any reason should have the burden of proof. They should be the exceptions.
What we should do is set a medieval status quo through game mechanics. It's fine to be different in some cases, and if you have an explanation for it, it's fine.
It shouldn't be fine to say "religion is for idiots. I'm so much better than you all." And I'm not exaggerating. This sentiment is really quite prevalent.
But I don't see how your suggestion would help with any of that. Rude text will only annoy people, it won't make them go "oh, gee, that's right, I'm an !@#$%^& and should join any random religion, even if I dislike it and it has zero content, because the game says so". I'd rather we work on making religions more appealing.
You do have a point, and I would hate to see the priest game killed, but having such an option would hardly stop me from traveling, RPing, and not following any military orders. Dunno about others, though, I guess it should be taken into account.
Power gamers, the scourge of every game...
If you are ordered to stay at the front, and threatened with fines and bans if you don't? Threatened to be kicked out of the religion if you don't?
I don't think the ability to give morale bonus means priests are automatically soldiers, does it? They still cannot be part of an army unless they already were in it before turning priests. It is also quite risky to bring priests into the battlefield, since they are so easy to capture. This would work more like a bonus at home which can trigger interesting RPs between the troop commanders and the priests.
The ones in charge might not care if they are easy to capture. Being part of an army or not wouldn't stop people from ordering them around if they deem it best for the war effort.
Increasing the odds of capture is something we should avoid. The priest game is already unappealing enough as it is, many religions having failed recently because they lost their last priest, and a great deal of religions limping on the work of a single or last priest.