I understand restricting the rules can be framed as excluding certain types of behaviour. But its a bit more nuanced in terms of neutrality. The network will still be neutral when processing within the newer and narrower rules (proposed by BIP110). But there will always be some kind of restrictions inherent in the protocol design -- obviously even now not any arbitrary data of any nature of any size can be 'processed' by the network.

Unity emerges from the complex interaction of nodes (and the software the owner chooses to run), developers, miners, users. Whether the new narrower rules eventuate or not, Bitcoin will remain and the unity of the network will reveal itself. Note unity doesn't mean any individual receives his desired outcome, it means an emergent order that everyone continues to works in line with.

Just some thoughts your comment prompted.

I'll give it ago, probably revealing my ignorance.

The spam-debate is said to be related to PoW. But, PoW has one crucial role, not related to spam (from my perspective). It simply coordinates the longest chain--nothing more. Of course blocks need to be in consensus to be included; so the next mined block is held to consensus by the node runners. A miner-node could submit their "proof of work" on a non-consensus block, but it will not be included.

Next, other protocols are said to have a centralizing effect because of the use of "social consensus". In the case of email, the protocol is decentralized; there are decentralized approaches to dealing with spam, I know people who run their own server without problems. Users choosing a walled-garden such as gmail, and gmail being hostile seems to be one of the bigger problems. I'm not sure where the centralizing effect comes from, likely users choosing walled gardens for connivence (?). If bitcoin had a walled-garden, maybe we could have a spam-free chain! But I am not sure it was the fault of "social consensus". If we had a "social consensus" to reject centralizing forces, we may had better systems/protocols.

I guess the argument is that fees are the spam mitigation (as compared to email which does not have fees). There have mostly always been(?) been >0 sat/vB fees. We have mostly always had spam.

The question is, how do we truly reject any centralizing force? There is a complex set of motivations and incentives. Fiat addiction breeds centralization.

For point 1, how do you think 'blank check' funding can be prevented?