I've asked a few friends who are management consultants this. Most say around 25-50% of their job is doing that. They don't view this negatively though because

I've asked a few friends who are management consultants this. Most say around 25-50% of their job is doing that. They don't view this negatively though because in many cases getting a reputable consulting group to tell you what you already know helps the decision actually get implemented. The rest of their time they spend doing things like collecting information that the client can't/doesn't want to do on their own.