It is a must to have butter on toast, if there was no butter the bread will be dry and it won't have hardly any flavour. Another reason why you HAVE to put butter on toast is because the butter melts into the toast and that makes the toast taste amazing!
If not for the delicious topping of butter, the toast I eat would be plain and boring. Food, in my opinion, should be defined and celebrated, not just monotonous. Butter on toast gives it a leap of flavor, and I crave that leap. If not for that delicious butter, I wouldn't eat toast. YES!!
Butter gives this yummy aftertaste that just makes bread taste lovelier as you chew, and it is a perfect complement to the crunchy and slightly sweetened toast.
I add butter to my pancake mix, I use it to saute vegetables and I add it to biscuits. Butter just makes pastry taste better.