Because he proselytized for the Unitarian Church at the time there was a huge debate, won by Daniel Webster (a Unitarian himself), over the church being funded in Massachusetts and elsewhere by state taxes.
Well, you're wrong. The Virginia Religious Freedom statute, of which Jefferson was the original author (though it was actually passed through the efforts of Madison) makes it very clear that Jefferson did NOT support Virginia state taxes being paid to churches. He called that "sinful and tyrannical, in fact."
So you'll have to come up with more evidence than that Jefferson "proselytized for the Unitarian Church" as proof that he supported having Virginia tax monies paid to the Unitarian Church. (Such monies would have actually been illegal in Virginia, precisely because of the Religious Freedom Statute of which Jefferson was so justifiably proud.)
I'm going to be off the FR boards for a couple of days, but I look forward to any quote you might find that overcomes my Jefferson quote that such taxes would be "sinful and tyrannical."