Totally have that specific fetish. Was chatting about it over >>9979
Its degrading to be used such a way, even human, but when its something monsterious or alien, it goes even deeper in that degradation spectrum. You ARE being used for your body and its capabilities. Forced to gestate something that isn't remotely human, yet your body does what it was designed to do and it doesn't matter what you think or feel. Then you can spin humiliation into all of that if you concern yourself with how others might look upon you if they discover you or what you are carrying.
There are so many reasons why, but generally most of those motives root themselves in some for of degradation and/or humiliation. How those two manifest are quite a colorful variety of… well darkness