Not a sin per se'...But it is useless when trying to understand the things of God...Or most things for that matter...
It's like having a book telling you every thing you need to know about a topic...So instead of reading the instructions, you close the book and engage your little brain...
Logic and reason are for people who don't 'know' something...It's nothing more than a guess and of course every one thinks their guess is better than the other guy's...And then brag about their brilliance...
If you've got the book, can your simple logic and learn some facts...
Right. Like when Christ repeatedly says, "This is my Body" you close your mind to the clear instructions in the book, because you "know" something that is not written. So you close the book, engage your little brain, change the word in the instructions from "is" to "represents", and obfuscate. Everything makes sense now that we know you think logic and reason is sinful.
It is a lot easier when you can simply make up anything you want to believe, "know" it with certainty, and don't have to use logic or reason to defend it.