The problem is (from what I saw) is that most people don't understand legal texts and it is not clear to them what is happening. I am always an outlier because I ask the questions and I would never sign an NDA like that. The company can't (and mustn't) control what I do outside of work so far as I dont involve its IP/know-how/patent/whatever.
Unfortunately, if convetional habit is for people to sign regardless and trust they'll get lucky or stay friends, then despite your reasonable intentions, you may still be hurting your position by refusing and absurd contract.
See also: EULA's, and really every contract ever between two entities of significantly different clout.
