I know there are many who use NFP as just another form of BC. However, there are some legitimate reasons to abstain for a short time in order to postpone pregnancy. However, it is necessary to reevaluate each month to make sure it is still an issue.
I know there are other couples like you out there that abstain completely. I'm glad that it is a spiritual thing for you. I'm not sure I like the "animal urges" comment though. It's as if you saying that a natural, wonderful thing God gave married couples is somehow ugly. I hope that's not how you feel.
Sex is sinful when it is not intended to create human life. There is no way, if you do not intend to conceive, to have sex in the full way intended by God. If you choose to only have sex when you are infertile, it is just as selfish as ABC. Therefore abstinance is the only moral choice for a fertile couple. And believe me, I'm incredibly fertile!
And in our wealthy society, there really is no good excuse not to have more children. One can always squeeze another into a bedroom, forgo vacations, home school, shop thrift stores. We all have so much.