It is better not to judge people

Morality is important only in how it affects people (both yourself and others).  

Judgement of people is detrimental to my happiness.  It doesn't sit well with my conscience.  My judgement of a person can also be detrimental to that person.  A person's attitude in an interaction affects the person at the other end. 

Then, there's the problem of inaccuracy.  How can I possibly know a person?  The more I get to know someone, the more I realize how complex they are.  They may be reserved around some, and outgoing around others.  They may be ignorant of some things, and savvy about others.  They may be blunt and rude, but kind and helpful.  They may be sweet today, and angry tomorrow.   My snapshot of them cannot possibly be a accurate model of who they are as a whole.  And my reaction to what I expect them to be will undoubtedly affect them when we're together. 

Also, isn't it human nature to greatly exaggerate differences?  Even when none really exist?

Some say that judgement of people and situations are important to ensure safety.  But how can you gauge safety by glancing at a person?  Not all safe people are well-dressed and not all dangerous people are scruffy.  Furthermore, is it that black-and-white?  Don't people change behavior in reaction to others?  Don't their behaviors change over time?   I always feel calmer around calm people and more agitated around agitated people.