About 15-20% of the general population is what's known as H.S.P. (a Highly Sensitive Person). Have a look at the work of Dr Elaine Aron if you like. These people have central nervous systems that are slightly more evolved and as a result they're much more sensitive to input stimuli (sound, touch, light, taste, smell, feelings, weather, etc.)
I'm one of these HSPs. Even with a well-extracted coffee, it is too inherently bitter for me to enjoy without sugar. I've tried to wean myself off more than several times but no matter how long I go without sugar I just don't enjoy coffee without. Life'