Angela...
I don't think it's necessarily sinful, but rather pointless.
In some cultures shaving for women is a religious ritual-especially carnally oriented religions like Islam.
My Spiritual Father is a Greek Monk, and on his advice I've stopped shaving, wearing makeup, and wearing pants. He didn't tell me to do these things, but upon asking he gave his opinion. These are all things that are of no use to the salvation of one's soul, so why do them? We wear deodorant and bathe as to not be offensive to others, but honestly if you're dressing modestly-who sees your legs besides your husband anyway?
When secular people ask me about it- I tell them I am a feminist, that I don't want to be a sex object, LOL. They get all flustered because they think that they are feminists, yet their whole goal is just to look "attractive" and let people judge them on this basis. I don't consider myself a feminist in the modern sense of the word, but it sure makes for interesting conversation.
Another argument I've heard is that all that all these things to make women like pre-pubescent girls (shaving of various parts of the body, the quest to obtain waif-like figures) is part of the general spirit of pedophilia in our modern American culture. Who knows.
Also disposable razors are REALLY bad for the environment.
In Christ,
Tessa