Hi.
More people are starting to make their private keys from strings of words. Wallets like MultiBit HD force you to create your private keys from word strings. If Bitcoin grew substantially larger, surely this would present a problem? I could create a program to randomly shuffle words in 24 word strings (the most words MultiBit allows to create a private keys with), to create private keys and check them for a BTC balance on the block chain. If the keys' address had BTC allocated to it, I could simply withdraw it to my own, untraceable wallet.

Is my understanding of Bitcoin correct in this, and if so, surely this could happen if most of the world's population used Bitcoin?