Human nature doesn't change. It's been the same since Cro-Magnons left Africa. We do behave differently in different situations and contexts, and as a result of different experiences. But, to my eye, that simply means that, if we'd lived in the right times and places, we'd be cheering at the Coliseum, or cutting hearts out of living sacrifices in Central and South America, or shopping for slaves in Charleston, or bringing offerings to the local ziggurat.
In other words, we don't get to choose our times, but our times define us. And as to politics, it's a matter of choosing your poison.
I agree that human nature does not change. With regard to the current topic, this is clearly a law which seeks to control not just human behavior, but thought and desire itself. It attacks the nature of self and desire, and throws echoes back to our Calvinist roots (nationally speaking). We fear and dislike not just what others might do, but what they think. I believe there is some hypocrisy there, because in order to fear what we believe they think, we must be able to imagine it ourselves. Our society is rife with clear and obvious examples of our own mass inner conflict regarding certain taboo subjects involving children and adults; it's used as mass-media and potent advertising, for God's sake. If many of us did not respond, it simply would not work, and we'd arrest and string up the advertisers.
Our (US) system of laws may have stemmed from a Judeo-Christian understanding of morals and the responsibility of the individual in society, but our founders took special care to limit the powers of government lest it run amok, and our laws are basically intended to be narrowly tailored, and to restrict unwanted behavior, not unwanted thought. A person is free to think what they will. But this law illustrates that when it involves some deep Calvinist taboo, many of us will cheerfully ignore such concepts in favor of restricting what a person thinks. In the case of this law, we acknowledge that the photos themselves are of no consequence - they would be legal if NOT taken 'with intent to arouse'. It is not the photograph we address, but the intent of the photographer, the lust we presume is in their heart (and it probably is in there, in this fellow's case). We punish the thought, not the action. But because we have no law to criminalize thought, we created a framework under which such a (presumed) deviant can be prosecuted.
This vague and catch-all law is bound to be abused, since as you said, it is left up to the tender mercies of people not qualified to know what is in a human heart and mind.
At the same time, normally rational people consider how they would feel if a person pointed a camera at their daughter. If the person were a pervert, they feel anger, disgust, and want them arrested. If the photograph was instead taken by a random ATM machine or traffic signal camera, there is scarcely even recognition that it happens, let alone furor. Everyone can easily understand WHY people feel protective way about their offspring, but no one can articulate what harm is being done that should be regulated by law. The damage they see is non-tangible. We have no crimes (other than this perhaps) that prosecute people criminally for making others feel bad, let alone send them to prison for up to two years.