I believe and I may be wrong that most guilds do some amount of chairitable work in order to mantain their "non-profit" status. While they raise money through shows, raffles and bingos etc. they have to give away a certain percentage in order to keep the IRS off of thier case. When any group has a bank account that sees the coming and going of thousands of dollars "big brother" gets very interested. I know both of the guilds I belong to have to pay rent and have ongoing expenses for speakers, teachers etc. When you are dealing with groups as large as 100 that is a given.
I participate only in the projects I choose. If I felt pressured I would not be a member of the group. I am also willing to speak up when I get that impression.