This was not exactly Homer's best line, or the worst shot at Unitarianism (I did whince at "Unitartian Stew": there's nothing in it). Of course Homer isn't much of an authority about faith of any type. However, I think the joke is SUPPOSED to be that, according to most Unitarians (including me) there is NO "one true faith"; God reveals himself to each of us as we are able to understand and comprehend Him. Therefore your faith is, presumably at least, as "true" as mine.
The final arbiter for all faiths is how well it works for and through you. Or as James, the brother of Jesus said, ". . .show me your faith without the works, and I will show you my faith by my works. . .faith without works is useless." James 2:18 & 20.