The problem with *sacred tradition* and infallibility is that if the teaching doesn’t line up with Scripture, it’s wrong.
If it does, it’s redundant and didn’t need to be repeated or be given the stamp of approval of some church council.
If it contradicts scripture it is wrong, if it covers precisely what is covered in scripture with precisely the same depth and nuance, it is redundant.
But there are lots of other cases. E.g. abortion falls under “thou shall not kill.”