Yeah not an easy one, but for some states it makes sense to have them as the cost of war for an aggressor increases so much worst case they wont attack and that keeps the peace. As NATO country they should be protected under some circumstances as well... But of course looking only at Germany alone against Russia it seems to make sense to get them but that is not the case at the moment... Potential arms races and MAD type peaces at the far end after spending huge amounts of money and effort getting there...