It's not unreasonable to see it as ideal, and it's not unreasonable for others to view it otherwise.
I've gone through having had a family member aggressively try to convince me to kill myself to make them happy and to stop me being a burden to them, resulting that I've spent most of my life having the thoughts that my death would make people happier than me living as I am. I've met other disabled adults who have gone through and deal with similar. I also grew up near where some of the horror stories in Canada around MAID have happened.
I'm not against the fully informed choice for adults as long as they can withdraw or the action paused, if they refuse at the time up until the overdose is taken. I don't think anyone, even with dementia, should be held down to administer the medication no matter what they previously agreed - consent is only consent if someone can withdraw it.
I am strongly against people in position of trust and authority offering that choice to often vulnerable people - people can be informed of their options without their medical professional or a government professional involved with them giving it to them. At the very least, we should be able to have it in our records whether someone opts-in to having those discussion, and having that as the default to reduce the risks
I do think fully informed choice does include that death by overdose, even if given by a medical professional isn't always the commonly portrayed go to sleep, don't wake up. It will almost certainly make it faster than most conditions/natural death, which is part of the appeal - but that doesn't mean it is always comfortable or dignified. Most do, but not everyone reacts to those medications well and people should be prepared like in other medical procedures.
Why do you think killing a 700kg mammal is easier than killing a 100kg mammal?
Because we do not treat people like other animals, and biology isn't just about weight. No one is using pentobarbital or any other veterinary method for medically assisted dying.
In all process I know, it involves giving a combination of sedatives, an anxiolytic to reduce panic, and medication to paralyse muscles which are all used for other medical reasons. It's known that not everyone reacts well to those medications individually, but the medical team or individual may not know that before it's given how the person will react. The sedatives and muscle paralysers are used at dosages to kill, and the body can do some distressing things in that process no matter the means. We can make deaths quicker, we can get closer to, but cannot guarantee it being the peaceful death many want or appear peaceful to family members there. Those who work with the dying have been preparing families for the potentially distressing happenings of death before medically assisted dying, and it's needed with it as well especially in cultures where dying has largely been given over to medical professionals.