A difficult concept for some, it seems.
A person I know, Catholic educated, repeated that "quality of life" argument to me the other day. It mattered NOT that Terri was not hooked up to a machine that might be considered extraordinary means. It was Terri's quality of life. It unfortunately did not bother my friend that Terri would be STARVED. "If I find myself in Terri's shoes, starve me and turn up the morphine."
You might notice one modality in the folks who support Terri's offing -- they are self-driven control freaks. They demand complete control of all their choices and happenings of life.
Having the responsibility of caring for a person long-term -- to give up so much of one's life to do so -- seems impossible to them, so scary, that they treasure the "bring me the dynamite" options of life, where such are available. Like in offing the bedridden, the addled, the cranky and crazy, the sickly, the barely-responsive burdens. That's just one modality --- there are others as well, other reasons why people side with the "loving" husband.
And that lover-boy? What is his motive? Very strange, imo.