In order to be convicted of a crime the accused have the Constitutional right to be tried by a jury of their peers. People from the same town need to be convinced (beyond a reasonable doubt) that a criminal act occurred. The defendant convinces one juror that it wasn't that bad of an act, not that deviant, victimless, not something he or she is willing to send someone to jail over - and you've got yourself a hung jury and the defendant walks.
Freedom of religion, speech, etc., (any 1st Amendment or other Constitutional rights) aren't absolute. The government can, and does, pass many laws that restrict said rights (like prohibiting shouting "fire" in a crowded theater). If the law is narrowly tailored to meet a legitimate government interest in the least restrictive manner than it will pass Constitutional muster.
Many laws limit pornography or obscenity ('perversions') - those guilty of obscenity fail the Miller test
Whether "the average person, applying contemporary community standards", would find that the work, taken as a whole, appeals to the prurient interest,
Whether the work depicts or describes, in a patently offensive way, sexual conduct specifically defined by applicable state law,
Whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.
As with juries, as with most crimes, it comes down to contemporary community standards. It's the way the law works...
- Ben.