It's a few minutes walk away, I wouldn't say right inside. The location is good, at the beginning of where markets start setting up along Sukhumvit. To be fair, most hotels along Sukhumvit are not too far from the two famous red light districts in the area, Nana Plaza or Soi Cowboy. I honestly had no issues with it being next to Nana Plaza - even when you walk out at night, you can walk right past that area with no issues, since Nana Plaza is tucked away in the soi it is located in. There aren't any noise issues from that area from inside the hotel.
It's not bad at all. I find that most people who go to Thailand for sex tourism aren't the type of people who will be staying at the JW Marriott. Less money spent on a room means more money for other activities for those folks. It's not like you will see a ton of hookers at this hotel. I certainly had no issues at all with the location. All the street vendors, markets, and I suppose working girls walking around - that kind of goes with the area, as far as Sukhumvit is concerned. A lot of tourists like being close to the things along Sukhumvit, along with all the things that come with it.