Who is there to believe?

Someone who has to write more than one page just to reply to a simple meaningless sentence, or the one who doesn't feel the need to defend himself? Why do some people find it so important to bring others down after a simple statement of someone that was harmless?
Update: Do people go into an attack mode because they feel threatened?
Update 2: This isn't about me.. it's about something I've seen happening to someone.
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