I know ISP's are not one entity. But they are all centralised in the way that each of them facilitate access for more than one singular user each. I believe that all countries have a cooperation between ISP's and governments, which have the potentiality of ISP's being used as tools by tyrannical leaders to silence opposition. That is the type of centralisation that is definitely not beneficial for humanity.
While you are right and ISPs may silence this and that, you're omitting that:
1. In a democratic country the ISP will go for profit, hence won't completely silence a customer.
2. If the ISP filters certain things then tunneling / VPN can, in most cases "fix" this.
So the ISP cannot create a perfect "wall" if one is... resourceful.
So while your suppositions may stand correct in a dictatorship, the rest of the world will just go as usual. And the rest of the world is big enough to not be seen as centralized (else we can end up to "bitcoin is centralized: one can mine it only from Earth" odd exaggerations).