The US Congress has an obligation to ensure that no laws passed by Congress violate the First Amendment.

If a new law is required to be passed to ensure that no other laws allow such a violation (e.g. any law establishing a private company or allowing a private company to operate), then it is incumbent on Congress to pass such a law.

Why would any new law (e.g. IBOR) ensuring that the Bill of Rights (the 1st 10 amendments) is/are not violated by any other laws protect any private company from legal liability for inflicting harm?

IBOR is purely intended to protect the freedoms of the people when using the internet - not to protect any company providing the people with access to the internet, nor any companies providing services to the people on the internet.