I felt that way too about euthanasia. I was dead set against it. Then when I was 20, my pet rabbit had some sort of seizure/stroke and was laying there half dead. Was I going to let it suffer? No, I took it to the vet and had him put to sleep. It was horrible, but it had to be done. To end the suffering.
Now my first dog came to me when I was 18. I had wanted a dog my entire life, but my parents wouldn't let me. They had plenty of dogs, and didn't want to go through the pain of losing another. So anyway, I got my bear, and loved loved loved him. I never could imagine having to put him to sleep. I used to think that people did that because they were too lazy, or selfish to take care of a geriatric animal.
Then last year, when he was 14, the vet told me that he was going into kidney failure. That he would slowly start to deteriorate. Then almost a year passed and he started having mini seizures, and completely lost bowel control. I loved him every second that I was cleaning up after him, or giving him his meds. Then one day, me and the kids and hubby woke up from a nap. I came downstairs and Bear was having seizures(mini ones) every minute or so. He had lost a lot of weigh. Barely ate anymore. And it just hit me, that I was keeping him alive out of selfishness. That I didn't want to lose him. Well, I made my mind up in that second that I needed to help him to the other side. There is not a day goes by that I don't miss him, or think of him. I NEVER regret what I did.
I am going through this with my big boy in the signature right now. It is TERRIBLE and I really don't know how I am going to be able to do it. But I know that I will if I have to.