No question that it could be used correctly. However, matheus23 already wrote code snippet which demonstrates how it might get mis-used:
All code can be used wrongly - what's important is how easily it can be used correctly.
You don't constrain an API on the sole reason people could attempt retarded things with it.
You could add a static variable easily in some class like "DeltaUtil", and call
DeltaUtil.update()
every game-cycle, which is doing the exact same thing:
[variable-name] = getDeltaTimePrivate(); // Maybe another name
and let getDelta() do this:
public double getDelta() {
return [variable-name];
}
That's it