How is someone supporting and fostering a bad act not also to blame? I see from your profile you work in adtech, perhaps rights shouldn't be decided by people who seek to avoid blame because they profit from it.
You have no idea about my background so let's stick to the actual argument.
Selling items and running ads is not the same as supporting or fostering a bad act. People can similarly buy knives or many other potential and actual weapons, it's still the user that's ultimately at fault.
When you run an ad for weapons next to articles inciting retaliation against the government, it does become the same as supporting or fostering an insurrection.
Now, sure, it can happen because you unleashed an algorithm on the world and don't know what it does, but you're still responsible for it.
Perhaps you want the government to tell you what you can say but I would prefer to go in the opposite direction and completely divorce speech from action, and stop trampling on our rights over the actions of a few. This endless shifting of blame solves nothing.
Selling items and running ads is not the same as supporting or fostering a bad act. People can similarly buy knives or many other potential and actual weapons, it's still the user that's ultimately at fault.