Knowingly manipulating people into suicide is a crime and people have already been found guilty of doing it.
So the answer is obvious. If you knowingly encourage a vulnerable person to commit suicide, and your intent can be proved, you can and should be held accountable for manslaughter.
That's what social media companies are doing. They aren't loaning you extremist ideas to help you. That's a terrible analogy. They're intentionally serving extreme content to drive you into more and more upsetting spaces, while pretending that there aren't any consequences for doing so.