Grassroots activism is great, but I think it's pretty clear that a single person at an elite think tank is more impactful than a single grassroot.
Now, if you think you can pull a Nelson Mandela, go for the activist approach, but most people can't, and 80,000 hours is in the business of giving advice to maximize expected utility.
The problem is that the single person's hands are tied because of their position. You can't influence the government from a think tank if you're suggesting prison abolition, banning cars from Manhattan, or even just massive social housing projects. Those think tanks would never get funded or get the time of day in government. Some things really need people power from below.
I think we're both completely correct. Some things need power from below, but those things are almost never the most efficient things to be working on precisely because they're so outside the political mainstream.
This is also the reason EA gets a lot of hate from various quarters. They take picking your battles to an extreme, and essentially come right out and say that many worthy causes are not the right ones to be fighting for.
Now, if you think you can pull a Nelson Mandela, go for the activist approach, but most people can't, and 80,000 hours is in the business of giving advice to maximize expected utility.