It's pretty significant to us, because we're here :) Seriously, from our point of view, including adriand's, there is something to be lost from Mankind's destruction because it would be the end of our entire species. From the perspective of the universe as a whole, it may not be significant, but it seems eminently sensible for humans to be concerned about it.
Also, it is possible that Earth is significant to the universe because it's the only place where intelligent life has arisen. I don't expect that this is actually the case, but so far we have no evidence to the contrary, and if it were true it would be tragic if we wiped ourselves out by playing with virii and nuclear technology.
500 years ago all human settlements on Earth had always been agrarian economies with different levels of development but primitive nonetheless, until the industrial revolution started.
What if it had never happened? Now we now there were previous attempts at industry, like steam engines and chemistry, but there was always a war, a drought or some other disaster that destroyed the framework where said developments were made, and sometimes even killed the people making them (Archimedes for example).
What if the universe is just like that? what if we're the most advanced species and all the aliens out there are either animals or still haven't even figured out how to build clocks or engines?
If that's the case then all the knowledge that ever existed would die with us.
Also, it is possible that Earth is significant to the universe because it's the only place where intelligent life has arisen. I don't expect that this is actually the case, but so far we have no evidence to the contrary, and if it were true it would be tragic if we wiped ourselves out by playing with virii and nuclear technology.