Suicide is not assisted, leaves a mess for those that discover a corpse, EMT's and others to clean up. Someone's suffering might end when they jump in front of a train but the train driver's suffering only just begins at that point.
Suicide is often an unmanaged, chaotic process which causes trauma. It also often fails whilst leaving those that attempt it in bad physical shape. A law like this reduces the necessity of discussing, normalizing or enabling suicide because there is a safe and properly counseled path out of a no-win situation for those that truly need it. A policy on containment when there are probably household cleaners that could do the job effectively with a small amount of chemistry knowledge is absolutely insane - and if someone truly is in that much pain, they'll find a way. Families and loved ones also have time to work through grief and loss rather than getting the wind knocked out of them when they hear the news.
The fact that we've hit a point where we can even have a discussion about this is probably something that should be celebrated, rather than being so totalitarian and controlling that we effectively force people to live even when they're in enormous pain.
I'd hoped nobody would come to the conclusion that was the core argument, but it is a consideration.
And I would like to draw attention to the totalitarian nature of our attitudes towards suicide. It's been enforced heartlessly for a very long time - if you commit suicide, you'll go someplace worse. It's this, it's that. All ultimately to remove the last escape for people who are in some form of extreme physical, mental, emotional or existential pain to the point where they don't believe there's another solution.
I'd sooner discuss why we have those attitudes - maybe it's so we get a free pass to be extractive and shitty whilst simultaneously denying the people we abuse even the dignity of leaving on their own terms.