How many operators of firewalls have both the time and the
expertise to truly understand several thousand lines of someone
else's source code? It may give you a warm fuzy feeling to have
it, but unless you're going to take the time to go over it
line by line and verify it, is it really going to help you?
Some people do have the time and the expertise and for them,
source is valuable and perhaps a necessity. For others, the fact
that the source is available may mean that someone else has taken
the time to verify the code.