Why does Catholic Church (and possibly some other denominations) approve natural family planning and condemn different kinds of contraception?

That's one thing that bothers me. While I agree that using means of birth control that affect embryo is simply wrong in the terms of morality, I cannot tell any difference between natural family planning and different kinds of contraception (as mentioned in the title). I know the argumentation that the first mentioned way is consistent with nature, while the other one is contradictory with characteristics of the true act of love. However, that doesn't appear to be really convincing to me. After all, preventing yourself from having sex in certain period of life also appears to be not consistent with nature - after all, it's act of human will (I'm not saying it's wrong, it just appears to be not different from other means of contraception). Also, I think that the intention of the action is most important factor of moral evaluation of it. Nevertheless, both the outcome and intention of using contraception in both mentioned cases are the same - partners don't want to have baby, and so it happens, though no embryo dies. Also, some people indicate that using, so to say, "artificial" contraception makes people more liberal in their love life. Actually, I'd dispute with that. After all, it's not impossible that individuals would be able to "control" themselves but just not bother with natural method of family planning. To sum up, I wanted to indicate that for me there's no actual difference between natural and non-natural birth control (excluding all the means causing early miscarriage). Can anyone tell me real difference between those two that could cause varying moral evaluation of these? Thank you in advance for all the answers.