Cardinal sin of brat preparation

We're having brats for dinner tonight, so I decided to look around the net to see the various ways people simmer their brats before grilling. A friend had served me brats towards the end of summer that had been prepared with such care prior to grilling that they almost literally melted in your mouth. The first place I went on my search was The Bratwurst Pages. The author was quite knowledgeable, but I found something there that horrified me. The author demeaned yellow mustard while advocating ketchup for brats. What a crime! Yellow mustard is fine for those who have no appreciation for mustards, but ketchup on a brat should never, ever, be allowed to occur. Friends don't let friends put ketchup on bratwurst. Mustard is a complementary flavor for a brat, but ketchup does nothing but cover up the taste.