Women love to feel small. They get on their knees for their man because they love submitting to his dominant figure. The act of fellatio symbolizes her subservience to his authority. Women who don't get on their knees for their man lack humility in regard to these reasons.
There is a reason people say "Suck my dick" to sound powerful.
I think when it comes to fellatio and cunnilingus, The only reason it COULD be degrading is because one of the partners makes it into a degrading act. Just the simple act can't be degrading. How a person approaches it could be. If it's forced, That's rape and is degrading. I actually wish the OP would have given more detail in the question. Obviously, They have been led to believe that it is degrading and I would be interested to hear what they believe are the reasons why. . .