Procreation and Un-natural....both weak arguments. We aren't here to just have kids and Un-natural compared to what? What the Bible says? With out the Bible and the guidelines in it you'd not know what was or wasn't exaclty natural or not. You don't know the stove eye is hot until you feel the heat. You don't know that it is un-natural unless something or someone tells you. You might not feel it is natural for you, but you can't make a blanket statement like that.
I'm trying to figure out how to answer this without being too graphic and I'm at a loss.
God built his laws of nature into everything, and even the people in dark jungles far from civilization figure it out.
But you can't say this with 100% certainty...free will is involved in everything. Because of this everything we deem as natural is just framed by what we know.
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"If we don't learn to live together we're gonna die alone"
Jack Shephard.