imagine earth will be in danger. instead of all humans die we will ever more humans on other planets.
imagine there will be humans in like 6 different planets, 1 planet being destroyed wont harm all of the humans but there will be survivors and lot of them.
The only thing that would make Earth less inhabitable than any other body in our solar system would be an impact of a dwarf planet, which is unlikely to happen within the next 5 billion and then Earth is doomed anyway. Your argument does not hold water. It doesn't matter much whether we go multiplanetary for this reason by 2024 or in a billion years.
Imagine Earth during the years after the dinosaur killing asteroid impact. It's a paradise compared to Mars or anything else in the solar system. And something like that only happens every 100 million years or so.