This just adds a tiny amount of friction to impulsive attempts, which may be a classic cry for help or just someone in the depths of some sort of mental health episode. Such folks may think better of it the next day and a very small amount of inconvenience will put them off. I think suicide is serious enough that you should probably mean it, and societally saying 'think twice about this' is a good thing.
On the idea that it just shift deaths, as your sibling poster points out (from the UK) -
"in the 11 years following the legislation there were an estimated 765 fewer suicide and open verdict deaths from paracetamol poisoning, which represented a reduction of 43% [...] This reduction was largely unaltered after controlling for a downward trend in deaths involving other methods of poisoning and also suicides by all methods."
https://www.psych.ox.ac.uk/research/research-groups/csr/rese...
So it looks like this tiny, tiny barrier does actually deter people. And that definitely points to them not really being sold on it in any rational way.