Yes, just the sheer numbers of them will be enough to possibly end this world as we know it-- Mao used to say he could easily endure 200 million casualties in any conflict...
The biggest saving grace is the squabbling & killing amongst themselves for now---
but pray that an event which could be characterized as "mystic", or a trigger / command from Allah(for most believe that there will be a world cataclysm, after which Islam will rule the world) does not occur-- and they all unite enmasse worldwide, taking over most of Africa, Asia, and chunks of Europe; with an evil eye towards the rest of us...... What will you do then?
Nuke, bomb & gas most into submission-- and in that process kill off most, if not all the rest of the world?