Something can be both "simply a job" and different than most jobs. The argument is that sex work isn't inherently immoral, so deserves to be supported by our financial infrastructure. It's "simply a job" in the sense that it deserves legitimacy, not that it's exactly like most other jobs.

Institutional support instead of prosecution also comes with the benefit of at least partially undermining the black market of the work, and the additional crimes that are frequently associated with sex work.