That sounds an awful lot like "If you've done nothing wrong, you have nothing to fear", a statement which I know is very much false.
What you think is disparaging may be very different from what your employer thinks is disparaging. By signing away your rights using ill-defined and imprecise language, you are only opening yourself up to potential legal troubles later.
I could flip your final statement on its head: assuming you don't desperately need the severance payment, agreeing is foolish.