The chemical isn’t the problem, it’s the dose. For instance, people have died from drinking too much water.
Sodium nitrite is used in cured meats to prevent botulism. I use half a teaspoon for 10 pounds of meat when I make sausage. It’s safe enough, at least, safer than botulism. Those people ingested way more to kill themselves, fully aware of the consequences.
It’s a tool. Like any tool, it can be used to harm, like knives, hammers or ropes. If we had to outlaw everything that could kill us, we wouldn’t have much left … Including water.