The First Amendment is a highly controversial one. The rights given all seem logical enough, and they seem to be rights that should be guaranteed to everyone. The real question becomes whether or not limits should be placed on these rights. For example, the Westboro Baptist Church pickets the funerals of military personnel saying that they died for a sinful country, and that the soldier is now in hell. Should this really be allowed? No matter what a person may think based on their morals, this is completely legal, and any law against it would be considered "unconstitutional". In fact, the U.S. Supreme Court just finished trying a case against the Westboro Baptist Church, Snyder v. Phelps. They ruled in favor of the church, despite how controversial its protesting may be. The First Amendment's job is basically to protect everyone's opinion, and to allow them to express that opinion in various ways without consequence.
By knowing the Miranda rights, a person would be better prepared to face law enforcement. If you are not read the Miranda rights when you're arrested, things you say cannot legally be held against you in a court. It all goes back to due processes, and knowing your rights within the legal system. However, as with any law loop holes can be found. In the case of, Berghuis v. Thompkins, since the suspect did not specifically say that he was envoking his right to remain silent, everything he said was admissable in court. The Supreme Court was split, but ultimately decided that the evidence was able to be used.