The Sex Talk to 250 students

I had been planning on giving a talk about artificial contraception and just the "sex talk" in general for one of my morning reflections for the high school I teach at.  I had fully intended to video it, but it completely slipped my mind. So I guess I will do my best to try to recreate some of what I said today.  The Holy Spirit was moving me and I honestly was surprised when the bell rang telling me I had run out of time.
I explained to the students I was not going to get into the politics of the HHS mandate; I was going to talk about what so many people did not want to talk about: sex.
There are 2 main reasons why artificial contraception is hurtful.  I explained that yes, it is a sin to use artificial contraception, and that it is because it hurts us, it causes damage to us as human beings.
I explained the first strictly Biblical reason why contraception is a sin.  Genesis 38, Onan is called upon to provide his deceased brother offspring.  He has relations with his sister-in-law but implores the old pull-out method and spills his seed on the ground.  For that, God strikes him down.  He got to enjoy the pleasure of the experience while at the same time not doing what he was called upon to do.
For those that are not sure about Scripture I then went into the natural law side of the discussion.  I did my best to explain that natural law tells that everything has its natural purpose.  Plants are intended to grow and reproduce, just like humans.  Sex has a twofold end; unity and procreation.  If any one of those is left out it hurts the organism, by not allowing it to reach its natural end.  I explained about bulimia and how a bulimic will eat and experience the joy of eating and tasting, but then fail to experience the next part, which is to be satisfied and full.  Or I explained how it would be like taking a plant and putting it in a closet and seeing if it grows or not.  When things are not allowed to reach then natural end, they are effected in a negative way.  I even went as far as to talk about how boys know what this feels like, when something isn't allowed to reach its natural end and the build up blood in a certain region causes a lot of pain (I was told by a few that they knew what I was talking about; blue-balls)
(Pretty much all of this info I took from the awesome blog Bad Catholic and his two blogs on "Why Contraception is Bad" ; #1 and #2)
The Holy Spirit really was moving me and one thing I threw in a few times that it is wrong to go past kissing before you are in a committed relationship with a ring on your finger.  Sex is a time when we get to be as close to God as we can be and get a chance to be like God and create life.  I also threw in my thoughts on the Dr. Oz show and the doctor who kept referring to the "risk of pregnancy" and how it hurt me every time she said that.
Honestly, I got only good feedback from my talk, both from students and adults.  I didn't do it justice at all with this post because when I am up there in front of the school, it truly is the Holy Spirit working through me, and we were fired up today and I got the message across that God needed me to get across.

Peace all