5. Remove canceling values (a - b) a + b = b
That's called dividing by zero. That's generally a no-no. Nice try though.
The government would include all the informaton that they know already and then you would fill in the rest =- the way this is set up, they don't put your taxes to pay in there. You are responsible to add in what else you earned, just like today.
True, you're "responsible to add in what else you earned", but if you know they can't catch you for it, what prevents you from not telling them?.
Another thing is... how do you know that the person filing the tax return is the person they're claiming to be? That would be one easy way to find out a *lot* of critical information about someone simply by requesting the governments tax return info so they can fill it out. (Identify theft anyone?)