I think that "charities" is too over-arching a term to have any meaning in this case. Eton, SPCK, and the RSPCA are all charities. Eton can invest as it likes, as I can't think of anything that would be against its principles of ensuring that to those that have shall be given. For the avoidance of hypocrisy, SPCK ought not to invest in firms profiting from abortion - not that there actually are any, unless all pharmaceutical companies are ruled out. Likewise, considering its broad supporter base and mission the RSPCA should not invest in Huntingdon Life Sciences, although as an individual I might have no problems with being a member of the former and investing in the latter. And though the Eton and SPCK are both charities, I consider them harmful to society and where they put their cash is the least of my concerns.