When we first arrived in our apartment (a little over a year ago now), I saw (and killed) a few mini roaches in the kitchen--very small, about the size of a bee or wasp, but flat, not round, of course. Brandon thought I was crazy to say so, but I did think they were kind of cute. They disappeared after a few days.
But Monday afternoon I came into the kitchen and there was a slightly larger roach, about the size of a cricket, munching on a crumb. And oh, my goodness, it was beautiful! It stood tall and moved about so gracefully on its long, delicate legs--and it was a gorgeous amber color. And so it was with a tiny bit of sadness that I crushed it utterly beneath the sole of my flip flop.
I sympathize with the principle of non-violence toward all living creatures (well, unless you count microorganisms--or plants, really). I think it's appropriate to have a tiny amount of sadness when killing insects--an amount of sadness tiny as the insects themselves, and short as their brief lifespans.