what is the name of the fallacy for when someone disagrees with something simply because they don't understand
The name of the fallacy is called the Argument from Ignorance fallacy.
explain it
The Argument from Ignorance fallacy occurs when someone argues that a claim is false simply because it has not been proven true, or that a claim is true because it has not been proven false. In other words, the person believes that if something cannot be proven one way or the other, they can dismiss it or accept it based on their lack of understanding.
This fallacy overlooks the possibility of alternative explanations or evidence that may exist, and assumes that lack of proof in one direction automatically implies proof in the opposite direction. It is important to keep an open mind and consider all available evidence before coming to a conclusion about a particular claim or statement.