I figured a contradiction in Kant's Universalizability principle, but I'm very surprised that it was so easy to prove that wrong, so I think that I might be wrong somewhere.
Let us first begin with a definition of his principle:
The concept of universalizability was set out by the 18th-century German philosopher Immanuel Kant as part of his work Groundwork of the Metaphysics of Morals. It is part of the first formulation of his categorical imperative, which states that the only morally acceptable maxims of our actions are those that could rationally be willed to be universal law. The precise meaning of universalizability is contentious, but the most common interpretation is that the categorical imperative asks whether the maxim of your action could become one that everyone could act upon in similar circumstances. If the action could be universalized (i.e., everyone could do it), then it is morally acceptable. Otherwise, it is not. (Wikipedia)
Here's my work:
If everybody eats potato in one day, then the world would be out of potato.
If the world is out of potato, then the action "eating potato" will not be possible.
Then eating potato cannot be universalized.
Then eating potato is wrong.
But eating potato cannot be wrong! Why? Here is the generalization:
For any x, if everybody eats x in one day, then the world would be out of x.
If the world is out of x, then the action "eating x" will not be possible.
Then for any x, eating x cannot be universalized.
Then for any x, eating x is wrong.
Then eating is wrong.
If everybody does not eat, then everybody will die.
Then the action "not eating" will not be possible.
Then "not eating" cannot be universalized.
Then "not eating" is wrong.
Then "eating" and "not eating" are wrong at the same time.
Then universalizability principle is wrong.
There may be a problem in the order of for all x for all y where x is food and y is person, however I think this is not my mistake, but Kant's. If we switch those places, then we have something like: "all humans should not eat the same thing at the same time", which is very different than universalizability principle as the statement do not consider the human equality. However, this does not create a contradiction.
Am I wrong somewhere or did I just prove that Kant's universalizability principle is wrong because "if everyone had the same duty, then the world would be contradictory, but if everyone had different duties, then there is no contradiction"?