Why? Because I say so! That's why.

The 'because I say so..' is a bad bear argument.

Why?  Because I say so! Only joking

"Because I say so!"claims status from the form of the command rather than the substance.

It is about who said something and not what

Because I say so! could be used to explain anything

Apart from the above bad reasoning, "...because I say so!", 

is faulty because  it claims to stand outside

the jurisdiction of normal criticism.  So there!