The Romans have a pretty bad reputation and they are notorious in history for their perversions and sexual orgies that used to take place on a regular basis. It is enough to have a look at some art pieces from the Roman period and you'll see that it is filled with sexual charge. There are male-male couples in bed, male-boy, male-female (mostly from Pompeii period), you name it and it's there.
It was only after the ascension of Christianity that moral changes took place. The new monotheistic religion came to an end to all this nude scenes from baths and luxurious villas. Christianity brought in a new idea of the afterlife which will come as a reward for a modest and chest life on earth.
By all means this changed the way people lived their lives, and it is probably the reason why we are so shocked to see this kind of scenes on the coins. From today's moral point of view it is absolutely unacceptable to have this sort of scenery on a currency.
Maybe the best way for understanding these scenes of lovemaking on a coins is to try and sweep everything that we today think is moral under a rug and try to imagine the world as it was then. Try to depict entering a luxurious villa and seeing on the wall of its best room sexual vignettes that showed much more daring acts than you saw in a local bordello.
In that sort of atmosphere with specific social parties and banquettes and daily ritual baths, it is easier to imagine that this sort of coins are being used. Especially, if you remember the fact that lovemaking scenes were everywhere from a cup and jug to plates, wall paintings, mosaics, etc.
However weird this may sound, maybe it was a bit more natural time and a lot easier and less frustrating period when compared to today's false morality.