burned every calorie eaten!

Long term, this could be a problem. For just today? Eat if you're hungry, and don't if you're not.

simple answer: yes.
you're giving your body nothing to run on if you just burn everything off.

Um yes this is dangerous. You already burn like 2000 calories a day, and then to eat and then burn all that off...its like eating nothing.

So your net calories for the day is zero? That's equal to your car being out of gas.

MFP is set up so that your daily goal has you at a calorie deficit without exercise - meaning if you ate to goal every day and did zero exercise, you'd lose weight. When you burn cals through exercise, you create an even larger deficit, which is actually counterproductive to weight loss, and leaves you with zero fuel at times, like today. That's why MFP adds those exercise cals to your daily goal when you log them - they expect you to eat them back.

Goal means goal, and food is fuel - eat too little on a regular basis and your metabolism will eventually slow down, and your body will want to store fat rather than burn it.