Even though freedom of speech is extremely important to our nations history, protesting at a funeral serves no legitimate purpose and is just abusing it like the Westboro Baptist Church does.
Freedom of speech is meant to be able to protest our government or other people but there is no need to protest the dead since they are no longer doing any harm that would be in need of protesting.
An amendment is needed and not just a law because the Supreme Court already ruled that protesting funerals is allowed in Snyder v. Phelps