First, that agreement only matters if you actually have a dispute with your employer. If you don't have any legal disputes with your employer, signing that agreement makes absolutely no difference to you. Secondly, your employer may lawfully terminate you or refuse to hire you for refusing to sign an arbitration agreement. Lastly, you will have an opportunity to challenge the validity of the signed arbitration agreement later, if and when it actually matters.
Thus, in most cases, it's not worth jeopardizing your job by refusing to sign an agreement that's probably not going to make much difference to you anyway.