Wondered if anyone Catholic could help with this question. We were discussing the growing industry around fertility awareness/ natural family planning (apps etc and different business models) with a Catholic neighbour recently and this occurred to me, but I didn't like to ask in case it seemed like I was challenging her beliefs as a Catholic - she kind of sidestepped saying exactly what she felt about the subject, and DH and I are from a Jewish background so we don't know much about it.
She said that 'natural family planning' was kind of the opposite of trying to conceive in that you abstain on the days when you might be fertile. What I don't understand is how is this different to using contraception really? What is the theology behind not using contraception? Is it seen as interfering with G-d's plan or is it because all sex, except that which may conceive a child, is somehow wrong (even between husband and wife?) Either way, I don't see how NFP is that different, in the first case, you are still weighting the odds very heavily against G-d's plan and in the second, you are only having the type of sex that is seen as wrong.
Please don't think I'm asking this to be oppositional about Catholic belief, I just want to understand another religion better and I'm a very small details person, so I just get bogged down in the logic of a situation and need to understand it.