Peasants not allowed to own weaponry? I'm not sure about that.
As for not being able to afford it, that depends on what you classify as a weapon. This is the middle ages equivalent we're talking about, there are plenty of wooden sticks to sharpen, farm equipment to use, etc. And recruiting a unit with 15% or whatever doesn't make you a savage at all. Just a different sort of common peasant folk the noble is leading.
Knights, lords, and dukes are ousted from their position all the time. Religion merely provides yet another rationale for doing so. (The others are primarily war and justice). And people defy the authority of kings all the time! Hell, that's kind of the main thing we do. Follow one king, kill another. Support one king, betray another (or better yet, the same king!) So it's hardly some sort of universal offense. And there are plenty of religions which would, could, or have in the past endorsed such behavior.
Farm implements and sharpened sticks are as to weapons as a super soaker is to a rifle. They are called "improvised" weapons for a reason. No one can simply outlaw anything that could ever be used as a weapon, because everything would be illegal. Swords, pikes, ACTUAL weapons were illegal for the peasantry to own unless they were actually serving in a capacity where they needed them such as being in the town guard.
Losing a title due to war or being convicted of an offense such as treason is ENTIRELY different than an unruly peasant mob lead by a priest with no legal authority forcing someone from their estate. People do not defy Kings all the time, and those who do usually lead short lives.
It stands simply that a priest conducting an auto da fae is violating a very principle law. Kings and Dukes give titles, no one else does. Titles aren't arbitrary things that come and go, and the only means to remove one is by force. When a priest forces a noble from his post, his is openly defying Kingly or Duchal authority, and would be arrested on the spot.
