To avoid a naive sibyl attack in most of the decentralized consensus protocols there is a scarce resources that needs to be use in order to take part in the consensus mechanism. This resource is computational power at proof of work and it is a kind of a cryptocurrency at proof of stake. Actually, consortium systems do not differ very much from this idea. In consortium systems, the scarce resource is the identity: only nodes with a special distributed identity are able to participate in the consensus. In this sense it works similarly as the public blockchain networks : the scarce guarantees that none with a huge bot network, but without the scarce resource can influence the consensus voting.
