[jillesvangurp]

This is one of those things that comes up frequently in discussions about Stellar. It's simply not true. It's neither centralized nor limited to a few partners. You can start your own validator easily. The way the Stellar consensus protocol works is that when you do that, you specify which other validators to trust.

The consensus in the network of validators is based on the network of who is trusting whom. Right now there are a few dozen companies running validators: https://www.stellar.org/developers/guides/nodes.html that trust each other directly or indirectly.

Most of the companies running these validators are doing so because they have business dependencies on the network. Running a validator is not actually free and comes with a bit of devops overhead. So you need a good business reason to do so as mining is just not a thing in Stellar. If you are doing business on Stellar, trusting your direct business partners is probably a smart thing. E.g. IBM and the banks they are partnering likely have ironclad contracts between them and good reasons to trust each other's validators. Most nodes also trust the SDF and trusting additional nodes for resilience is basically something you can do based on your judgment of who is running those nodes and how well they are running them (up time).

Lots of new nodes start with a default configuration that includes the Stellar foundation's own nodes. This is a bit of a problem. Stellar foundation is actually considering shutting down their own validators at this point as there are now plenty of reliable other validators around that they don't need to be there by default anymore. Over time, the number of validators and companies using them is likely to grow substantially. The network gets more robust as the network grows organically.

Of course for a malicious node the trick is getting others to trust you back. This only happens when people actually trust you. This makes e.g. 51% attacks really hard because you can spin up all the nodes you want but if people think you are a scammer, your nodes won't have any decision power. Mostly that's a good thing. Stellar is very resilient against this kind of thing; unlike other networks.