Some people are worried about the purity of the Gates Foundation investment criteria.
There are only degrees of purity. Once you start down this road you will find that no enterprise is pure and good, and all have, at least from someone's perspective, basic ethical flaws.
Name a company which you think is "good." I bet you that someone can offer a very legitimate argument (i.e. it has some real claim to rationality) as to why that company is in fact deeply flawed. Consider a national home-builder. Some might claim that simply on the basis that it builds suburban housing tracts then that alone is enough to diss it. What about a fast-food restaurant which pays its workers very well and offers health care, day care etc etc? Yet it supports by its location on suburban strip arterials the very worst sort of sub-urban expansion.
Now are some companies worse than others? Probably so and the intention to get rid of the worst is fine. But if you start looking carefully, you'll find that it is the very nature of civilization — human relations and resource use — will provides legitimate if not conclusive argument as to the depravity of the enterprise. (Of course human relations and resource use are at the root of all good things which civilization does, too.) Even an enterprise as seemingly benign as, for example, Patagonia (outdoor gear) contributes to our society's infatuation with fashion and image.
Sure, get rid of cigarette makers. What about people who make candy? And which encourage obesity, which is also a killer? No, I think this effort to find "good companies" is not as simple as it appears.
UPDATE: A commenter accuses me of raising a strawman. I do nothing of the kind. I suggest that the task urged on the Gates Foundation is a futile one and that none of us should engage in futile behavior. Unless a corporation is doing something illegal on a massive scale, there is no reason except pique and/or personal preference not to invest. There are many vegans in the USA and in Seattle. Should Gates refuse to invest in a meat-packer? Because it slaughters animals? Or Wal-Mart because of its suburban site-planning practices? I simply don't see a moral imperative. If we don't like the behavior of a company, then makes its behavior illegal. Let's go a step farther. Suppose Gates can find NO equity investments which are "worthy." It then puts it money in US Treasury bonds and bills. Don't you think it is helping to lower interest rates? Yes it is and thus making the cost of doing business for nefarious corporations that much cheaper. (To boot it is aiding GW Bush in his absurd overseas fiascoes.)
The only way in which moral-based investing might be effective is to flip it around so that the Gates did nothing but buy positions -- using its massive endowment -- in companies so as to change their policies i.e. it picked out the "worst" companies (and you'll have big debates about that too) and bought huge positions so as to explicitly change management and its policies. I am not suggesting such a course but it would be more effective than the namby-pamby of "we are too pure to invest in you."
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Others are also skeptical about "SRI": Is socially responsible investing a sham?