I'm not sure why lemon juice would be gross, but you are correct that it is needed to keep your bananas (and apples) from turning color. Its a chemistry thing.
If you want to see for yourself, try this experiment (which uses an apple but it works just as well with a banana):
1. Cut the apple in half from top to bottom.
2. On one apple half, lightly coat the white part of the apple with lemon juice. Leave the other half uncoated. (The uncoated half is your "control" sample and let's you see what normally happens to a cut open apple.)
3. Observe the color of both apple halves, then place them white-part-up on a counter or tabletop.
4. Observe the apples again after 30 minutes. Notice any color changes and/or differences in appearance.
5. Look at the apples again periodically throughout the day. What do you find?