Sometimes people take different sides on 
different matters, and "harsh opinions" (NOT
flames) may make the poster seem rude or 
"out to get" people.  By remaining anonymous
(and still remaining civil, even if the opinion
may be harsh) the poster can avoid having a 
negative association linked to his or her 
name.

Sorry, Yann, I don't agree with your "fear of
endorsing their opinions" statement.  In the
"online world," opinions of another person are
completely based on what is read, as other
e-users have no chance to meet the person and 
find out more about their character, integrity,
etc.  A handle often (if not always) helps
other e-users to recognize someone and form an
opinion about that person based on what they
have read... and not all opinions are nice.  By
allowing free speech and giving the poster the
chance to remain anonymous, the poster does
not have to worry about the consequences of
expressing a less-than-popular view.

Just my two cents.  =)

Lady Z