A while back, I complained about the ACM's membership in the AAP, a publishing trade organization that supported some odious legislation like SOPA and the Research Works Act. The ACM, to their credit, responded to the concerns that the community at large raised (there were many others). ACM's Director of Group Publishing Scott Delman did so in this space, and ACM President Alain Chesnais did so on his blog. (Side note: in that post, and especially in the comments to it, Chesnais seemed to come really close to saying something like "The ACM does not and will not support the RWA, SOPA, or the AAP's lobbying, because the ACM doesn't take political stances in either way as a matter of policy" but he also seemed to take really great pains to not say anything that clear and specific, which was baffling to me.)
One of the arguments I used in that previous post was about Author-izer, the new ACM service that allows you to provide the official version of your papers for free from your personal webpage. The reason I brought that in to the argument is that Author-izer is basically a good idea insofar as the CS community trusts the ACM to act in their interests. I still support the argument that their membership in the AAP runs directly counter those interests and thereby necessarily weakens that trust. Certainly, though, life's complicated and everyone gets to decide as an individual if they want to be a member (and thereby a supporter) of the ACM despite their affiliation with the AAP, just as the ACM as an institution gets to decide if it (we!) want to be a member (and thereby a supporter) of the definitely-lobbying AAP despite having a no-lobbying policy.
Andrew Appel, at the Freedom to Tinker blog, has a series of three blog posts presenting four ways that academics can think about their relationship to copyright. I had fun reading them, and they provide an interesting alternative answer to why trusting the ACM to act in our interests is important. The model that Appel suggested that he subscribes to sees signing away one's valuable research papers as a significant charitable contribution. He's comfortable giving that charitable contribution both to ACM and IEEE, presumably because he broadly supports them and their roles, and because the cost to the world as a whole of the donation, relative to just making the donation truly free, is maybe not all that large. (I could note that reviewing papers also fits well within this model of charitable contribution.)
The idea that adopting this view is a reasonable compromise, as Appel suggests, seems pretty reasonable to me, while remaining sympathetic (and potentially responsive) to concerns "that ACM and IEEE have fallen behind the curve." I certainly try to donate to organizations I believe in and trust! I would therefore certainly pause before making a in-kind charitable contribution to a highly profitable Dutch multinational that spearheads legislation like the RWA and lends credibility to homeopathy, but that reflects my values and doesn't need to reflect yours.