I'm all for it. I'm really glad that Oregon - my lovely home state - supports peoples right to choose to do with themselves as they see fit.
To say that it's selfish to decide to end your life when you have a horrible illness just because your loved ones will suffer is... well... incredibly selfish. They're going through a lot more pain than you'll go through with their passing - which is often inevitable - and forcing someone to be subjected to the painful, agonizing, and often incredibly embarrassing symptoms of a lot of these illnesses is just awful.
I totally agree with Karkat - it's their life, and it should be their choice how long they participate in it and how.
On the other hand, it wouldn't necessarily be selfish for family, friends, loved ones to support the possibility of better health and vitality that their loved one may receive if they hung on a little longer than choosing to cut their life short before seeing treatment is working or that they are much more mentally stronger than their physical/physiological problems than they actually think at the moment of deciding brain death. It's like they've may have progressed so far despite suffering to not see the light that things are getting better. Seeing it from loved ones' perspective say kids of a parent with type 2 diabetes, diabetes has many health implications that make can life unbearable from poor blood circulation, etc. However many live with diabetes despite their ailments to see their kids grow up in a good environment, support family and friends, continue to pursue life aspirations like earn a master's degree and travel. Loved ones truly who love someone aren't thinking for themself but for the loved one suffering maybe just now who will be cured or better or learn to live with a not terminal illness/disability because there's other success stories that show it's possible and their own life they can create anew despite their not totally degenerative health condition. That there is still life past, through personal suffering due or not due to health conditions that are not totally degenerative or at least yet. I understand if it's time to go it's time to go, but people whose time it's not to go can still be and not make the illness/disability hinder them more than it just does.
I understand a patient's choice thought long and carefully if rational about opting for brain death if their are very low hopes of survivable and persistent debilitating suffering that's just getting worse, but it can also be considered selfish to just let someone kill his or her self if there is very high hopes of survival and overcoming personal health conditions. I just don't see killing yourself as a necessary priority as a patient or regular person. All in all suicide is truly a person's choice. Sometimes "suffering" isn't necessarily something to take on at face value but something inevitable and to take in stride and overcome honestly with all strength and support had if possible. I just don't see suicide assisted or not always acceptable, due to the possibility and usually there is if chosen to lead and live a better life regardless of a certain illness or disability. Then loved ones have a reason to help their suffering loved one keep realizing that for his or her own sake to not give up all hope.
It can be seen as selfish, to choose to die or not die or for loved ones to let a loved one die or not die. In the end, it depends on the circumstance and likelihood of survivabilty, ability to maintain health despite conditions, and will of the patient. Not all cases do patients need to immediately opt for death, where it may just be a downswing of their condition. Death is finite and can't be reversed once chosen. I'd say only when one is definitely going to die soon, and/or immobile, constantly mentally physically suffering on all levels that he or she can't handle then the choice for brain death is totally acceptable whether we like it or not. If mobile, not as constantly mentally physically pained on all levels, able to survive, overcome, or be cured and willed to be better, an illness that can be toughed out, why not make the most of life despite it because things can be worse.
I don't know I sympathize for both sides, really but I support life overall.