Punishment is a legitimate disincentive. Are there going to be fewer prostitutes when it is safe and easy? If the field is inherently injurious to women, why should we incentivize women to become prostitutes in any way?
They are not protected by regulations, they don't receive pensions and they don't pay taxes.
There are a lot of jobs that might not be the best life choices. But that's no reason to make it illegal and force the people performing these jobs underground.
It sounds like you just have a problem with sex in general and protecting women is about as much a goal of yours as when politicians cry "think of the children"