In many places second floors are necessary. Certainly if you have a two story you'd notice the stairs missing.
Many drown in lakes, ponds, and bathtubs. Bathing is far more a necessity than keeping around an suicide/accident machine.
second floors are not necessary
the abundance of single level dwellings tells us this
and I specifically mentioned swimming pools not lakes and rivers
and one does not need a tub as showers are always an option
Stairs are sure necessary if you have a two story house, and we have lots of them. How do you elimate two stories in crowded areas? Many cities have neighborhoods filled with them and small yards.
How do you eliminate lakes and oceans? Very young children do not take showers.
Now getting rid of guns, that would be easy by comparison. Most wouldn't even notice. Are you not getting it yet?