Being a nerd is nothing to be ashamed of. Nerds rule the world! Who invented the internet? Nerds. Who created personal computers and smart phones? Nerds. Who made every video game you've ever played and ever will? Still nerds. Who sent probes to distant planets? Nerds, nerds and more nerds! I'm a nerd and I'm proud.
Well, even if you go on peaceful, you have to deal with horses and cows. All you want to do is build! Well, just customize the presets. Chane the world from grass to lime or green stained clay or green wool if you have to. That doesn't enable mobs to spawn. And- it looks like grass. I'm sure there's plenty of tutorials on how to customize presets, and are plenty of websites that you can customize the world, then the preset will automatically be generated and you just copy and paste.
This thread was created in 2012. I don't think the OP even reads it anymore. People posting "/gamerule doMobSpawning false" This command did not exist back in 2012. And the OP may be already using it. That's if he / she even still plays MC anymore.
These threads should "auto lock" after a year of inactivity.