Is euthanasia really a bad thing?

Yes, I get it, it's illegal, but does that mean it's wrong? I understand that taking the life of another human is completely unacceptable, but what if a loved one of yours is in pain, whether it be physical or emotion? In the case of a terminal illness, that person is not going to get better, but instead is going to spend the last few months of their life in a struggle. Why not end their life for them so that you can remember them for the good memories, and not the ones you made whilst having to wait on them hand and food without another option?
I'd be interested to hear anyone's thoughts on this particular topic!