"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
The First Amendment guarantees the right of freedom of speech, or allowing anyone to say what they want and express their opinions freely. Legally, no one can stop you from using bad words. While some states still outlaw some forms of profanity, many of these laws are being nullified as violating the First Amendment (see here). Bleep! is not saying that you can't use bad language; Bleep!'s mission is to show you how negatively it reflects on you and that you should try to refrain from cursing as much as possible.