thinning seedlings

I just stood at my kitchen sink thinning seedlings from pots of herbs I've started that sit on my windowsill. It was very difficult. I felt like a murderer. I felt like the surviving seedlings were tilting towards me with an accusatory look. Which led me to wondering, "How on earth do people make decisions on selective abortion"?
How could a mother look at a womb-full of babies and say keep that one but expel this one?
Just wondering...