I can tell you exactly why I think this way - if you believe that there's an all-powerful superbeing that rules everything and demands your worship and respect and you believe you should worship and respect it, then you should act in a way that respects it. Human cultural norms throughout history have had some emphasis on specific types of dress for certain situations, and not adhering to these norms is oft considered disrespectful. You treat worshiping your deity like going to a concert, and dress accordingly. This is an indicator to me that you don't give a damn about God, and just want to go out and have fun. You make church service about you. I still think you don't take your professed beliefs seriously. Heck, have you even finished reading the Bible cover to cover yet? You've had ample time since we had that conversation, but you probably haven't bothered - is the word of your god too boring for you to bother? I don't really give a damn that you don't dress up for church, I give a damn that you don't take your own beliefs seriously. Intellectual sloth like yours is a blight upon humanity.
I don't know how many non-believers are like this, but I'm sure that some of them don't like going to church
exactly because they see people who don't dress up for it (thus indicating that they don't take church seriously).
