Why should I? "When you judge others, you do not define them, you define yourself." Your opinion is just that, your opinion. And your opinions are like some passengers who believe that if you'll just "talk enough," the bus will finally go where YOU want it to. No dice. I just called out "my stop." ;-D
Behavior doesn't just "happen". It comes from decisions, conscious and unconscious, and tells the world about a person. So if I see a man with a chicken on his head, I can indeed judge his decision to do so without defining myself as anything other than an observant human being.
Actually, some opinions are more reliable than others. It depends what you base that opinion upon. If they are based upon nothing more than feelings, wishful thinking, and limited anecdotal evidence gathered in a provincial environment such as academia or the arts community, then they tend to be wispy and ephemeral. These are the kind of opinions one hears from adolescents of all ages.
If they are based upon facts, history, a keen understanding of human nature and broad life experience, they tend to be more solid and enduring. These are the kind of opinions one tends to hear from mature individuals.
When I was young, my opinions were like the former, and I thought my parents and other mature individuals were narrow-minded and old-fashioned. After years of honestly comparing opinion to reality, I have come to see their "opinions" borne out more often than not.