Postyle, I would add one more factor to the three factors you provided:
"* sales display lack of confidence in future stock prices * sales bring compensation issues to the foreground * sales dissuade individual/institutional investors as well as analysts"
I think the reason most shareholders are upset when there is massive insider selling is because insider selling almost always has a positive correlation with declining share prices. Insider selling is typically the event that marks the turn-around of rising IDCC share prices for many months to come. Of course just because it has happened that way so predictably in the past doesn't mean this time will be the same but it's a correlation that's too predictable to ignore.
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