The only justification I hear when I question this is a) "this is some
kind of proxy security mechanism for our clients" (really!) or b)
"whats loose source routing anyway?"
I've actually heard a third one, which is "I don't want someone to use me
for transit without paying for it." When I asked, "did you catch somebody
doing that?" they said "well, no, but it seems like a big hole anyway."