A lot of people feel like Trump is not mature enough, nor has the capacity to be president. He has said some things in his campaign which illustrates him as immature, and irresponsible, thus, unfit for presidency. Trust someone with these qualities with nuclear codes and things could go south.

it is just scaremongering atm but those that are doing it know that it can escalate into WW3 - which is what they want - so they go on and on about it all the time

Time for some history, the cuban missle crisis for example. What you got now is fairly normal, just out of proportion due to your election season