When I look at the story line, I don't see it as being sexist. If anything, it is reverse-sexism because only females can attain this power (at least, that's what I'm assuming, as you talk about birthing familiars, which would be hard for males). It's easy for people to pick on one small detail and argue against the greater flow of a book.

However, there is something worth thinking of here out of universe. You say "there always has to be a cost," and you are looking at fertility as that cost. That thinking could lead you to write a story which does have sexist content along the lines that people are warning about. If that's just one of many costs a witch pays, then you probably wont run into trouble. However, if this is the only price that's paid, and the fact that a price is paid is important to your story, then that is indeed making the suggestion that fertility is a major part of the value of a woman.

On the flip side, I think it would be completely feasible to write a story which turns this whole sexism argument around. You could easily write a story which strives to show that women are far more than just their reproductive organs with the same basic premise. I can envision a storyline where the majority of people value a woman's reproductive capabilities too much and their other attributes too little, confining them to strict roles accordingly, and the whole storyline revolves around a group of women who prove those people wrong, through many means of which witchcraft may be one of them.

When I look at the story line, I don't see it as being sexist. If anything, it's reverse-sexism, because only females can attain this power (at least, that's what I'm assuming, as you talk about birthing familiars, which would be hard for males). It's easy for people to pick on one small detail and argue against the greater flow of a book.

However, there is something worth thinking of here out of universe. You say "there always has to be a cost," and you are looking at fertility as that cost. That thinking could lead you to write a story which does have sexist content along the lines that people are warning about. If that's just one of many costs a witch pays, then you probably won't run into trouble. However, if this is the only price that's paid, and the fact that a price is paid is important to your story, then that is indeed making the suggestion that fertility is a major part of the value of a woman.

On the flip side, I think it would be completely feasible to write a story which turns this whole sexism argument around. You could easily write a story which strives to show that women are far more than just their reproductive organs with the same basic premise. I can envision a story line where the majority of people value a woman's reproductive capabilities too much and their other attributes too little, confining them to strict roles accordingly, and the whole story line revolves around a group of women who prove those people wrong, through many means of which witchcraft may be one of them.