No team should beat us. But Washington shouldn't have beat us last year after that great win against TB in week one. However the Saints inexplicably came out flat and unmotivated to start that game out. They should've easily handled Washington that week, and it set a theme for the rest of the year.
You can't account for when a team just comes out bringing less than 100% for whatever reason, but it happens. It will happen eventually this season, and the mark of a Super Bowl team is the one that can come out flat and still eek out wins. But don't make the mistake of thinking that every week this team will come out firing on all cylnders. It never works out like that.