Does the LessWrong community have a consensus on the subject of moral accountability, to the same extent that it has a consensus on things like free will and reductionism?

I don't know if this is a matter of consensus, but I generally see it as a matter of translating from third-person deontology to consequentialism by way of third-person virtue ethics and game theory: rather than work with concepts like "culpability" directly, I ask first whether an act is evidence that someone's likely to do other bad acts, and how well that risk can be mitigated, and second whether punishing that sort of act would make it rarer by enough to outweigh the cost and damage of punishing.

What you say is true to some extent, but there's also the fact that holding people morally responsible actually changes their behavior, and if we didn't hold anyone morally responsible for anything, people would behave worse.

their behavior is completely contingent upon their neurochemistry, which they have no control over.

People do have control over their neurochemistry. Invoking the classic compatabilist conception of free will, if they wanted to have different neurochemistry they would.

There is actually an article here titled Causality and Moral Responsibility. You may want to read the linked prerequisites first.

Moral Accountability is a lot like justice: It has a lot of psychological hooks in the human mind that make it very useful for enforcing how you want your society to be, and in the ancestral environment was probably linked far more closely to utility than it is today. The on margin effects of either cultural edifice might be good or bad but we should be careful about trying to dismantle either one.