According to Sikhism, hair is beneficial spiritually, and thus it makes sense to respect this aid to us. Alcohol, Pot, Cancer and a burst appendix all represent things that would cause you to regress spiritually, hence as a Sikh you do your best to avoid them. This is the essence of it. I feel I should've mentioned the slanted bit earlier.
That's your personal opinion being projected as fact now. The second part doesn't contradict anything that I said. If the universe proceeds according to God's will, then God has everything to do with it. It's a matter of whether you agree with that notion or not.