That’s part of it, however they are also against it from a morality and ethical point of view, with the central argument being that you can’t take an innocent person’s life, no matter how “good” you think your intentions are.
Basically they uphold the value of life above all else, including one’s desire to end it. By the same token, they are against any form of suicide.
citing individual cases is not the road to reason here IMHO. Every single person dies at some point. This is an "entire population" question. Ethics and Morality play an educational, character formation role.. and, a medical decision is not the same as other kinds of decisions.. Another point -- people who are unstable or overwhelmed personally often leap to extreme, graphic and emotional examples first and without context. The original post here fits that description IMHO
This is emphatically not an "entire population" question. This is an individual rights question. I don't know what safeguards exist in other countries to prevent "people who are unstable or overwhelmed personally" from "leaping to the extreme", but in Canada the rules are strict and multiple doctors have to sign off. You can read the MAiD eligibility criteria and the approval process here[0].
Basically they uphold the value of life above all else, including one’s desire to end it. By the same token, they are against any form of suicide.