Museums as Money Laundering Institutions
I am not sure how such things work in the UK, but here in the US companies get tax write-offs for charitable contributions. There may be PR benefits as well. (My view is that you ought to be able to either take the tax credit or have your name publicized, but not both.) And I have little doubt that 'not offending the sponsors' works its way, insidiously and unself-consciously into the minds of curators and artists.
The questions I have for the letter writers (whose complaints about corporate funding I largely endorse) is this: How do you differentiate clean from dirty when it comes to vast sums of wealth? Sure oil companies are an easy target. But where do you think all those wealthy patrons who buy your product (whether that be art, writing, labor, expertise, creativity, vision, or whatever) for galleries, magazines, catalogs, museums, concert halls, and so forth got their money? Do you think the funding that pays your rent is sanitized in some way?
On this matter I live in a glass house. I work at a University that gets funding and does business with all sorts of disreputable entities. All the Colleges and Universities where I studied keep similarly sketchy company. So, I am in the same boat. I think we need to dispense with the moralism. What precisely is the alternative you propose? Government funding for the arts? Some sort of list of 'socially responsible' patrons? (How, in constructing such a list, do we decide which sins are the most egregious?) The art world (and the intellectual world more generally) is, let's face it thoroughly infused with commercial and political pressures. What is the alternative you are proposing?
P.S.: I know that Solnit is among the signatories to the letter.