As much as I agree with Kyle's sentiment, I can 100% understand Jack's position here. In addition to wanting to remain eligible for movie and tv roles, he probably also doesn't want to get shot. Security for singers is probably more lax than security for ex-presidents, after all (at least most of the time). It's easy to imagine some troglodytic cultist piece of shit taking the band joking about killing their bloated lord and savior personally, and resolving to do something about it.
On the one hand, I can get where he's coming from on a humanitarian viewpoint, that praying for someone else's death is in the abstract a bad thing.
But to break up a band that's been going for like 25 years and that was the foundation of his entire success over something that could be equated to being a jovial quip either means that tenacious d has other issues as a band or that Jack Black has some political opinions that are more important to him than his friends.
I hope he gets a wake up call and attempts to repair the relationship with Kyle Gass as soon as possible.