Well, sexual liberation is/can be part of a feminist movement.
I guess you mean "slutwalks"? Let me give it a try:

People percieved as female are often shamed for their sexual life. On the one hand "man" make a great fuss about getting women into bed, at the same time she is a "hoe" for doing so.
At the same time everywere around you are (nearly) naked bodies in advertising and film etc so female sexuality and nudity is okay as long as it is for the "male gaze"

These walks want to accomplish two things:

First reclaiming the own body. Making a statement that it's ones own and that you are free to do with it what you consent to. (also in a sexual way)

Second (something that is more overlooked) it is often also a protest against the sexualisation of female bodies. Not just because women want to walk through the world without being seen as a sex-object on every poster they see, but also because it does serious harm when something happens to them (see victim blaming, "what was she wearing" "well she shouldn't..", "such a lean on")

There are many critic points in this (for example that it tends to be a white movement) but I think it's good to look at the problems these movements come from and try to understand why they are doing this

so thanks for asking