For those of you that have been living under a non-pixelated rock (the ones in real-life, not the ones you’ve carved out of generated mountains), then you should know that Minecraft has no storyline apart from the fact that monsters want to eat your eyeballs and you must fend said monsters off.
These monsters only appear in dark places such as caves, or at night, and will inexplicably spontaneously combust if they hit sunlight. Apart from Creepers, who sneak up on you and blow up.
Why do these monsters want you dead? Because they are monsters, and that’s all they do. I’m voting for the patch where we see the history of the race of Zombies or the background to the Creeper species and find out that they were brutally mistreated in past times by Humans, sold into slavery and abused