But it isn't a valid point unless it's backed by something useful. If all an argument has to stand on is that its opponents can't use carnal reasoning then there's no sense in having any reason in the universe at all.
I could claim there were pink unicorns dancing around the bushes at the end of my garden, and reject all questioning by saying "I know in my heart they are there" and telling people they are using carnal reasoning. We could do the same about the dragons that fly around my town. I could be a great prophet speaking the words of God, and write off anyone seeking to test my proclamations by claiming they were using carnal reasoning. Whatever stance you want to take and support with vague comments about not using carnal reasoning falls down because I could take the exact opposite stance and support it using the exact same argument. Any time one argument supports two diametrically opposed viewpoints we know something is wrong. But then maybe that too is carnal reasoning.
Serious question, when that sort of approach just results in everything and nothing being true wouldn't you rather have an objective standard of truth we could all fall back on at the same time, rather than having different people proposing different things (some sensible, some so far out it's not funny), all insisting that they know in their hearts that it is true and all insisting that anyone who opposes them is using carnal reasoning and just doesn't "get it"?