Look at any protocol or network service designed to be fully decentralized. Inefficient routing, unstable communication, high latency and low bandwidth. You have to do a lot more work to achieve things that would otherwise be simple and straightforward.
Take human communications, for example. They're largely decentralized by default, but we use centralized services to improve efficiency. If some piece of information needs to be disseminated to a large population over a period of time, we first record the message, then we post it in a centralized location viewable by lots of clients[1]. Those clients can then go back and distribute the information to its connected peers[2], but technology also allows us to distribute subscriptions of this information to a wider population in a variety of media[3]. ([1]stone tablets, [2]town crier, [3]newspapers/television)
Modern people are afraid of centralization in the Internet because they are suddenly realizing they have no real control over the content or medium. But this is the case with all other forms of centralized mass communication, too. People are also afraid of their lack of control over their data, which is tantamount in these days to a form of property. Anyone would freak out if the contents of their house were suddenly only available at the discretion of some conglomerate!
But you don't need "decentralization" to keep a backup of your data. Most of it originates from you anyway, and you can store it before you publish it. Some service providers even provide methods to download all your data, though obviously you can't rely on everyone providing you that option (unless someone passes a law...)
On top of all this, the internet is already a system of decentralized networks and services. You can just hook in your own services into the network at any point therein and maintain them yourself. The only restriction is really by the ISP, and there's lots of those to choose from in most developed countries. Personally I think we should consider the internet a combination of utility and public highway, since at this point we all need access, but we also need competition due to the sensitivity of limits on network access.