I don't have an issue with it necessarily - however - there is a shameless self promotion overkill point - keep it under control (eg 1 or 2 links per site) and you should be fine
Also continually offering another avenue for free porn does nothing to help sales - so consider only doing it on low yield pages (eg your warning pages). This sort of linking is primarily an S/E play imo - you won't see an overwhelming amount of traffic from such links.