The exchanges and miners do have a large influence, but the node runners (the users) have a voice as well. The node runners can get together, and refuse to peopogate the blocks of of the miners/exchanges that are being bad actors (BIP 148 for example) and also (BIP 110) that's currently making the rounds.

If a large enough percentage of the node runners need refuses to propogate a block from a bad actor, then another miner can mine the same block and get the reward.