Of course it doesn't serve them right.
Prison, for foreplay? Who exactly were they hurting?
Of course they are excessively stupid, but I don't think we should put people in prison for being stupid. Of course the law of the land should be followed, but when the punishment is disproportionate to the crime (as it is in this case) we should recognise it. They should have had a big fine slapped on them and been deported, thus losing their fancy tax free jobs as well. That would seem enough of a punishment to me for mere lewdness, but then, I'm not a muslim patriarch threatened by the concept of sexual enjoyment outside of marriage and obsessed with controlling everybody else's sexual behaviour, so lewdness doesn't actually bother me that much.
This couple didn't rob anyone, or threaten anyone, or make anyone feel bad. They weren't unkind, or frightening, or violent. They were just sexually incontinent, drunk and stupid. We'd have to lock up most British friday night pub-goers if we applied the same standards here. (Perhaps we should? Oh no we can't, there aren't enough prison places are there? OK scrap that.)