So let's say a group of nefarious miners consorted to place a fake block on the chain. Then there would be two blocks to follow... how do miners proceeding to the next block choose which fork to follow? When there are two possibilities, it would seem that it would be trivial for every miner to notice that there are two options and recalculate each one to select the correct one... oh yeah, half the minors (the nefarious ones) would select the fake block, and so on, eventually overpowering the true block.

Right?