A CMaj7 chord has both a B and a C in it and it sounds perfectly fine. You're saying the home chord in the key with the simplest extension is dissonant. That ma

A CMaj7 chord has both a B and a C in it and it sounds perfectly fine. You're saying the home chord in the key with the simplest extension is dissonant. That makes no sense. You hear music with two adjacent semitones played together all the time. It's in all jazz music and everything derived from it, which is a huge chunk of modern western music. Seriously, music isn't all just 3-note chords and a B and a C together sound perfectly fine in the right context, and even moreso when they are separated by several octaves, as in the mains hum theory.