Consider the sex workers who deal with mentally or physically disabled adults. Most people have sexual urges, and those who are unable to participate in society in the usual way of addressing their urges with a romantic partner or a one-night stand still have them. There are a good number of very professional sex workers out there who can provide these people with sex (often with specific expertise for the relevant handicaps) and generally significantly improve the wellbeing.
Are those sex workers doing something they shouldn't be doing?
You are asking a binary question for which there isn't a binary answer. Better to ask are those sex workers doing something they will get a pat on their backs for from other members of society? In a way a builder, chef, firefighter, and even a prison guard would.