The question is in the title though I would also add what do you think (those who have any issue with birth control) of someone who is on birth control for medical reasons and not for contraception per say. Is she still "sinful"?
Let me preface this by stating that I am a Christian. I think birth control is a personal decision and it is one that I do not see as inherently sinful. To me, these can come in the form of: condoms, medication, implants, sterilization, etc.. It is something I may find myself using at some point. I do take into consideration that, besides sterilization, there exists a chance (albeit a small chance) that pregnancy can still occur. That is a risk that I, personally, would feel comfortable taking -- and my husband will as well (if he is anything of a thinker). If it is God's will that I become pregnant, even if I am on the Pill, use a Nuvaring and have my husband put on 2 condoms (not that that would ever happen.. just sayin'!), then so be it.
I, personally, don't feel that birth control is immoral. What I
do feel is immoral is to go on about one's sexual endeavors without the least bit concern over pregnancy (considering we are strictly discussing heterosexual sex here). If you do not wish to become pregnant, do what you can to prevent it from happening (but realize that it still
can happen with the exception of sterilization). There are so many different choices for women these days. If you do not wish to have children for at least a few years, try the IUD. If you never want to have any children, perhaps sterilization is the best choice. If you'd rather the stand-by classic, try the Pill.
Having said all of that, I do not agree with practices such as the morning-after pill and abortion as a method of birth control. In fact, I am adamantly against them for this particular purpose. Birth control shouldn't be an after-thought, like grabbing a tissue after you sneeze. Pregnancy deals with bringing
life into this world. It is something that should be taken seriously and not haphazardly. Although abortion is a bit of a tangent (though not entirely off-the-mark), I still believe it to be a woman's choice to be able to make that kind of decision and that abortion is sometimes used as a last-minute alternative to a pregnancy derived from a negative or illegal experience or in cases where it is used to save a mother's life. I respect it as a choice, although I do not agree with it fundamentally.