If you build a bridge and make it open to the public, then you absolutely have both an ethical and legal obligation to make it safe to use.
people who have come to rely on my bridge start being unable to use it because it randomly drops them into the river.
That would be at least negligent manslaughter in most, if not all jurstictions.
To be clear I'm not saying that anyone has to do everything that that people request of them. But rather that there is a non-zero amount of responsibility to the public when a project is being actively maintained. If you don't want that responsibility, then let someone else take over, or announce that the project is abandoned.
Where I live if you build a bridge that is assessable to the public and someone gets hurt using it, because you made it unsafe to use, then you are legally responsible for that. It does not matter how many signs you put up, or what agreements were made, if you build a bridge (or other structure ) you are responsible for ensuring that it is safe to use.
Also, to clarify, it's not my analogy. I was using the one made by the person I responded to.