Utilitarism over everything else. That's my code code of coduct.
Why the hell would I waste effort in burial if I can just as well throw the bodies down the chasm? At least it'll show the others what they're getting if they dare to die in my fort. Killing kittens is also perfectly reasonable, since I only need a specific amount in order to keep the vermin population down. Anything else is just wasted food. The smartest thing to do, of course, would be to restrict the fort's feline population to only males or only females, but even then you'd have to be vigilant about the cats migrating into the fort.
But there are two sides to my approach. I don't, for instance, kill "useless" migrants - arranging the means for their termination would either be a waste of labour and time (i'm a neurotic fort architect, I always embark with 6 miners and there's bound to be something at works most of the time) or put my useful dwarves in jeopardy somehow, such as when gathering them to a platform and dropping it to a chasm (the miner could get hurt). And magma... i don't trust that shit. Too many obsidianized forts in the past. So instead, whenever I get unwanted migrants, I send their useless asses down to the coal mines to breathe on lignite dust and die off when it's their time to go. That way they still contribute to the fort economy and spare my real miners from black lung.
But, you know. Sometimes that little bit of elf in me says I could treat my people a little better. So I like to justify the need of maximal efficiency to myself by embarking to freezing tundras, glaciers, wastelands and deserts.