HELLO--TAKING MORAL THEOLOGY IN COLLEGE IS A MIXED BLESSING. EXPLAIN HOWW BIRTH CONTROL IS AGAINST NATURAL LAW,BUT EVERY PARISH PRIEST THAT I KNOW WILL ALLOW IT IF YOU HAVE 4 CHILDREN?Is this an actual question or are you just venting? :D I know it's frustrating anytime a priest gives you advice that is contrary to the teaching of the Church. We go to priests for their wisdom and spiritual direction. We shouldn't have to worry about whether or not what they say is actually true. So, I can see why you would be a little perturbed.
As for why a priest would say something like that, we can only speculate. It could be that he received inadequate formation in moral theology (especially if he was a seminarian in the 60's and 70's). A lot of priests had a difficult time with Humanae Vitae when it first came out, and I think it had a lot to do with what theologians and professors were teaching at the time.
Some people disagree with the Church out of a deliberate act of disobedience and others are simply ignorant of what the Church teaches (or they know the teaching but they have not been exposed to the arguments in defense of it). I know that some people will disagree with me on this, but I think that when it comes to priests, we should give them the benefit of the doubt and never assume that they are being purposefully malicious.
Also, never assume that you are better than or smarter than your priest. If he needs correction on a doctrinal or liturgical matter, approach him with humility and the utmost respect. "Father, I thought it was supposed to be like this, can you help me understand?" If the priest is your professor, bring it up once, as a matter of clarification. If it requires more conversation, meet him in his office. Never berate him or belittle him.
I hope that helps.