Given that Jon said,
"m-1 is always greater than 1-m"
we want to find how true the statement is;

secondly for negative values of m;

So, the statement "m-1 is always greater than 1-m" is false.
Because 1- m is greater than m-1 when m is a negative integer.
Therefore, I Disagree, because 1- m is greater than m-1 when m is a negative integer