Decentralized - a system in which no single person, institution, or machine is telling others what to do. It is open and transparent, where in a decentralized system participants interact one on one with each other. Thus with the very high integration and interaction of the participants, the possibility of an attack by a system hacker is very low, as the hacker has to go through all the participants systems to hack a single crypto-network, making the attempt harder than before. Also, there are no crucial central control points to attack. The economic size surrounding the system is much larger and therefore much more expensive to attack. In a nutshell, I would say decentralization is needed for a better security and trust as no single person or entity controls the system.