What difference does that make? If a child was buying this this chemical from Wal-Mart and the cashier checking them out said, "Oh, looks like you're trying to commit suicide. Have you considered buying some medication to keep those toxic chemicals down, or a book that will walk you through everything?" wouldn't you find that at all problematic?

If we can hold companies liable for what their employees recommend, I don't know why we wouldn't also hold them liable for what their recommendation engines recommend.

Mens rea makes the difference.

“People also bought” is very different from “It looks like you’re trying to suicide, let me help”.

If you ask the hardware store for a rope rated for an impact force of $X, they do not know your intentions, and they are not responsible for them. If you harm yourself, you’re culpable, not the store that simply sold you rope.