Many other countries have succeeded at bringing school shootings to zero, providing the fundamental feasibility in principle. That makes the difference.
The difference in America is that Americans really don't want to. By the time Sandy Hook happened, Americans had already long decided as a culture that they were willing to trade the lives of their children to protect their sacred right to keep and bear arms. Hell, many are happy to, as long as the kids aren't theirs.
Sort of. Sandy Hook meaningfully changed polling. Americans broadly support the idea someone should do something. Of course, they get colder feet when it gets more specific.
Regardless, this makes it very different from a 0 suicide or 0 spyware goal. Those don't have a similarly reasonable theoretical solution.