I'm thinking of feeding my cat glass shards.
Oh my gosh! That would be dangerous, don't you think?
The cat does not deserve to live.
As a pet owner, you are supposed to love and take care of your pet. You should feed your cat healthy food. If you don't want your cat anymore, then you should give it up for adoption instead of doing something that will cause it to die.
It's my cat, and I can do what I want with it.
You have a responsibility to your cat and it's well-being and giving it glass shards so that it will die is harmful, cruel and a breach of your duty. Treat your cat with the same respect that you expect from other living beings.