A red light district is for sex work. Sex trafficking and sex work can be distinguished (i.e. one can have sex work without sex trafficking).
Note that this contradicts nearly all official usage of the term "sex trafficking", which just refers to sex work. Far and away the most common kind of sex trafficking is a woman working independently trafficking herself.
https://humantraffickinghotline.org/what-human-trafficking/m...
The less legal sex work is, the more underground it needs to be. The more underground it is, the less recourse women have to address exploitation.