BI don't agree that the tax shows any sign of "weakening" religions yet. I question whether it is wise to do so; and if I did want to then starting a nondenominational house of learning or supporting the bill of rights with its promise of increased humanism would be more direct tools. From the tax all I see so far are priests getting angry. It's not an annual trade-off, but discontent pop-up events like this are likely to continue.
I disagree with the blanket statement:
they historically only ever seem to cause us grief.
Yoe I, our founder, pretty much built the kingdom with the might of the Alldivine mercenaries. Yoe II was also helped, although introducing a Professional Army severely limited that option. In our time of greatest need, the War of Dwarven Honour, they rescued Cyl yet again and even gave him a discount in the financial aftermath. So the Alldivines have been cool.
The Pantheonists have mostly made requests for building funds that we have been pleased to grant. The closest thing to causing "trouble" was
indirectly contributing to the death of Yoe II by calling their Great Hunt (which he might have avoided), and the withdrawal of Ustwelf from politics (so far we haven't needed him back, and I think there's more to that story that he refused to say aloud). Meanwhile our firstborn son, Leath, is enshrined in the Pantheon. I would think that distinction if anything strengthens our dynasty.
The Singularists have kept to themselves to the point I forget they're around unless specifically named in a Council like this.
The others in our empire (Enyntheism, Damed, Eleveners, and whatever Herta's Albion religion is formally called) occasionally got into spats with the big 3. But with the publication of Religious Freedom even those have trailed off. Alongside the proclamation from the first religious Council that recognized no one of them was strong enough to be the state-sponsored faith, our guarantee of free worship has done more to curtail organized religion's "problems" than I see from the tax.