Those kind of laws are very difficult to enforce, however in countries were similar laws are in place if for example you want to stay at a hotel with a person of the opposite sex you will need to stay in different rooms, so this could raise the costs for couples which are not married or for friends, which could indeed reduce tourism, however it would be interesting to see what has been the effect in other countries which have passed similar laws before.
Actually this is not too difficult to uphold in my opinion, especially when talking about Indonesia where most of the population has the same belief and of course the majority of Indonesian citizens have a religion which clearly prohibits this. I don't think this is difficult.
As for the actual impact, it doesn't really affect me in my opinion because it depends on the intentions of the tourists whether they are only visiting for sex or indeed for other business purposes because when they say business and sex are two different things. We live where we have rules and when we are in this case we cannot rule out rules that are prohibited either by law or religion unless you really don't have both in you.
Don't think too much about what happened in Indonesia, let's look at something that happened the last few days at the Qatar World Cup which made several rules that invited pros and cons in many circles. We can see now, if they really intend to watch the World Cup live in Qatar then there is no problem for them, but if they come with ulterior motives then this is a problem for them. But have we seen that the World Cup this time was not a success based on the rules that have been made? I see this is a successful World Cup.
It's the same with Indonesia, but everyone must respect and appreciate the rules that apply in these countries. There is a saying "where the earth is stepped on, that's where the sky is upheld".
I asked in return, don't people who think this regulation is a problem when there are tourists who don't respect what is valid in their country? Simply put, when we visit someone's house, we must respect and respect the rules of the house we visit.