I don't understand why your country allows dogs to die in peace but does not grant humans the right to choose their own end. Here it is normal that someone says: "Ok, lets end it." And the morphine is increased slowly while you don't eat and drink. The fact that there is no evolutionary pressure to make death less painful does not mean your should experience the full effects of it. I mean your country does offer painless births (something my country is very hesitant in, I have no idea why, oh cultures...)
You answered your own question - because they are dogs. We also do not allow people to crush other people they consider pests, like an ant or a fly. Human life is considered of higher value than insects or dogs.
Perhaps I should clarify that "someone" means the person him or herself. Would you really say no looking someone you love in the eye while they ask you to end it?
If you equate "relieving from unbearable suffering" with killing you must also equate not doing this with torture imo.
You value your own morals over the request of another, equal human being. To me that is your fundamental human right and I will not judge you for it. But I could not live with myself knowing that I denied someone I love their strongest wish while there is no cost to me personally. I'd feel incredibly selfish.
Just curious, would you actively stop someone in unbearable pain form killing her/himself or would you stop them? Would you help set up a machine to help someone kill her/himself?
Again, not judging, just loving this discussion and I'm willing to change my mind.