Is it proper to join non-mandatory professional groups?

Many professional organizations provide great benefits to their members; educational opportunities, professional conferences, networking, journal subscriptions, insurance, and product discounts. However, many also engage in lobbying of government officials on issues both related to the profession's direct interests and on issues only loosely associated (i.e. funding for political candidates). While some of this lobbying can be viewed as professional self-defense in an immorally regulated industry, where does one draw the line? Is there a point where joining professional associations is providing sanction to activities you believe are wrong?