Ben Kuhn sums up how Scott Aaronson sums up my thoughts on divestment

Aaronson:

I’m sensitive to the charge that divestment petitions are just meaningless sanctimony, a way for activists to feel morally pure without either making serious sacrifices or engaging the real complexities of an issue. In the end, though, that kind of meta-level judgment can’t absolve us of the need to consider each petition on its merits: if we think of a previous crisis for civilization (say, in the late 1930s), then it seems obvious that even symbolic divestment gestures were better than nothing.

What made up my mind was reading the arguments pro and con, and seeing that the organizers of this petition had a clear-eyed understanding of what they were trying to accomplish and why: they know that divestment can’t directly drive down oil companies’ stock prices, but it can powerfully signal to the world a scientific consensus that, if global catastrophe is to be averted, most of the known fossil-fuel reserves need to be left in the ground, and that current valuations of oil, gas, and coal companies fail to reflect that reality.

...

These realities [that averting more climate change requires extraordinary political will] have a counterintuitive practical implication that I wish both sides understood better. Namely, if you share my desperation and terror about this crisis, the urgent desire to do something, then limiting your personal carbon footprint should be very far from your main concern. Like, it’s great if you can bike to work, and you should keep it up (fresh air and exercise and all). But I’d say the anti-environmentalists are right that such voluntary steps are luxuries of the privileged, and will accordingly never add up to a hill of beans.

Let me go further: even to conceptualize this problem in terms of personal virtue and blame seems to me like a tragic mistake, one on which the environmentalists and their opponents colluded. Given the choice, I’d much rather that the readers of this blog flew to all the faraway conferences they wanted, drove gas-guzzling minivans, ate steaks every night, and had ten kids, but then also took some steps that made serious political action to leave most remaining fossil fuels in the ground even ε more likely, ε closer to the middle of our Overton window. (...)

Kuhn:

I used to think the arguments about whether to divest from fossil fuels were basically just silly -- after all, in a remotely efficient market it shouldn't affect the price! I've since gained somewhat more sympathy for them as it became clear that divesters by and large understand this charge. It's really not much different from more standard forms of protesting like standing around waving signs.

Of course, I'm still skeptical of the efficacy of divestment, just like I am about the efficacy of standing around waving signs. And I think it's possible that divestment campaigns do some harm by reinforcing a personal-virtue framing of environmentalism (with the "you're morally responsible for what you invest in, even if your investment doesn't have any causal effect on their activities" framing that's very common there). But I don't think they're totally misguided -- it's at least potentially defensible to argue for divestment on consequentialist grounds. (...)

So in summary, I agree with Ben's two paragraphs verbatim.

Also, do consider giving up farmed meat in addition to any agitating for divestment, sign-waving, or letter-writing you feel compelled to do. You'll make more of a (personal) impact than turning off the lights, using mass transit, and taking shorter showers combined, and be pulling sideways on a relevant policy rope.