I hate killing anything. I don't even kill a fly, I will shoo it out of the house.
However, years ago we lived in a house which backed onto fields. We had a couple of mice in the house. They used to sit on the hearth and stare at us.
I used to think, 'Oh, how cute', and no intentions of doing anything about them.
A few weeks later every food item in the pantry that was in a chewable container had been bitten through. We had mouse poo on the kitchen worktops. I bought plastic food containers but the poo was turning up all over the kitchen. We tried to block the bottom of the pantry door. You would not believe how narrow space a mouse can get through.
It was the poo everywhere that bothered me the most. I was told that mice wee continually when they are running about. This also made me feel that our health could be at risk.
We got the humane traps as I didn't want to kill them. They didn't work.
I desperation we ended up the with old fashioned traps - with peanut butter. We caught around six mice on the first night. I was shocked as I thought we only had a couple. In total we must have caught at least dozen mice over about a week.
Apparently, if you have one mouse and leave it be, you will end up with a house full.
A few months later we were pulling an internal wall down whilst doing some renovations. It was a hollow partition wall. There were about half a dozen mouse skeletons in the wall space. They had been there well from before we lived in the house.
As I said, I hate to kill animals but it gets to the point sometimes where you feel you don't have an alternative.