Perhaps an argument against this would be the resource usage, the amount of
paper used when you leave mistakes on the page is so much more. Think of the
trees! Then again, erasers either come from trees or petroleum so you’re going
to be using something either way.
Efficiency aside, there is a sort of philosophy that really needs to be
acknowledged here. We’re all taught that nobody is perfect, that we all make
mistakes. So why, then, should we go out of our ways to erase the mistakes that
we made? If we cover up our pasts are we not doomed to repeat them? For the
sake of our own educations is it not better of us to keep record of how we have
done wrong and to then build up an immunity to such failures?
Mathematics, especially, require proper procedure to succeed. There are steps
one must follow to achieve in math. If you cover up your mistakes, then you are
covering up all the pitfalls that caught you along the way, all your past
deviations from the path, and therefore allowing yourself to run along blindly
once again, vulnerable to these dangers. Why do this to yourself?
There is nothing wrong with using a pen to do math, in fact, it is for the
better that we all do so.